I'm gonna be as complete as possible. I've been playing KoF for 10+ years. It's up to you whether or not you trust me.

I'll assume you actually want to "win." Of course, this doesn't mean you tie a monkey to a chair and play that as your opponent over and over, even though you can "win" pretty easily that way. I guess a more accurate thing to say is that I'm assuming you want to *win as consistently as possible over an infinite number of games versus any potential opponent that might walk your way.* This game's pretty good at letting you do that, if you put in the time.

That also means that you have to play the WHOLE game. You can't just quit and say "you cheated" every time someone picks a top tier - that's only learning a part of the game.

If I had to summarize KoF into three points, they'd be these:
1) Strong universal systems. Once you learn the game with one character, you've basically learned 90% of it with every character. That doesn't mean the game is easy, nor does it mean you'll run out of things to think about anytime soon.
2) Movement is fast and powerful. You know how, when you play a Marvel vs Capcom game, and you pick Magneto, you can zoom all around the screen three times in 7 nanoseconds? KoF is kinda like that, too. The game's fast, and you can attack from several different angles at several different timings. While the opponent can attack any particular spot on the screen they want to, you can also just not be in that spot when they attack it, since you can move elsewhere, or you can try to intercept them on the way to that spot with a preemptive attack of your own. That's a basic summation of the "neutral" of this game.
3) Raw 50/50 mixups exist, but are not strong enough to build a gameplan around them by themselves... unless you pick Clark. The thing is, there are characters without overheads and command grabs and ambiguous crossup setups, and, in most games, that would automatically make them a bad character, but, in KoF, that's not necessarily the case. You don't have to hit the opponent right now - you can keep attacking, and they can keep blocking, but, eventually, they have to actively try to get you off of them, otherwise their guard gets broken. They can't just block their way out of your pressure - they can maybe two or three times, but, on the fourth time, you're just going to get a free combo.

Guess what - I already have a bunch of guides for this game, just not on Steam. You can read them here: https://moqlnkn.wordpress.com/kof-xv/

This will effectively be a summary of all of them. Anyway, let's get started.

There are 39 base characters, plus 13 DLC characters in the first season pass. All of them are competitively viable.

You need to pick a team of 3, and select their order. Your first character will start by facing the opponent's first character, then, when a character loses all of their HP, the round is over, and the winner's character moves on while the loser brings in their next character. The first to lose all three characters loses the whole match. If the timer runs out, the round ends instantly, and the character with higher health remaining is the winner of the round.

At this stage of your development as a player, your character choice does not matter - pick who you'd like. Every character is a rushdown character, but there are also five characters that have strong long-range projectiles, too: King, Andy, Athena, Rugal, and Joe. Angel and B.Jenet are by far the trickiest characters to learn, but they don't really bend the rules in any way. Again, pick who you'd like, in any order you'd like.

The game registers 8 directions and 4 buttons. Those are technically all you need to play the game, although you also need the start button to fully navigate the game's menus.

Let's start with those 8 directions: up, left, right, down, and the four diagonals. You'll need to understand Numpad Notation - thankfully, I already have a guide on that, which you can read here:
https://docs.google.com/document/d/1QHGQA-kSDtDBJ_vWF7MfpjRJGdyLHQ6f38o_raDjJ5Q/edit?usp=sharing

In simple terms, just look at your numpad. 5 is in the center, 2 is down, 8 is up, 6 is right, 4 is left, and all other other odd numbers are diagonals. In fighting games, most inputs aren't thought of as "left/right" but rather "front/back," so take that notation and change all the lefts to backs, and rights to forwards, so that 6 is forward, 9 is up-forward, 1 is down-back, etc. This will stay true even if your character switches sides. If your character is on the left side, 6 is right, but, if you're on the right side, facing left, 6 is left, because 6 is always forward.

Press and hold any of the upward directions (7, 8, 9) to jump. Jumping is nice, but you're on that set trajectory, and you can't really defend yourself while up there. Only a few characters have ways to alter their jump trajectory, and not by much. Anti-air is a very important thing to practice.

Tap an upward direction to do a short hop. These don't go as high and don't travel as far, but are in the air for much less time, effectively shortening your vulnerability period. Some people have trouble performing hops at first - you have to tap and release very quickly. It's just something you'll need to practice until you can do it every time. Alternatively, you can tap an upward direction and then quickly hold a downward direction, if that's easier for you.

Tap a downward direction right before hopping or jumping to do a hyper hop or super jump. Performing hyper hops, i.e. tapping down then tapping up, is the trickiest form of movement that you need to learn. These don't add any vertical height to your hops/jumps, nor do they add any air time, but they do increase the horizontal distance traveled. Likewise, you can't super jump or hyper hop straight up, because there is no horizontal distance traveled at all - it wouldn't do anything.

Hold left or right to walk... walking's cool, but slow. Double tap left or right to dash in that direction, which is much faster. Back dashes are immediately airborne, and can be used to dodge the opponent's low and throw attacks. Forward dashes are non-committal, and you can cancel them at any time into any attack or jump, even immediately - it's even possible to forward dash for one frame before inputting an attack. During a forward dash, if you keep holding forward, you'll continue to run indefinitely, even if the opponent jumps over your head. The same is not true for back dashes.

Holding straight back (4) or down-back (1) will BLOCK. If the opponent's going to attack you, you can just block it to negate all the damage. You obviously cannot block while attacking, or doing some other action, including jumping. Certain attacks require you to block a certain way. "Low" attacks require you to crouch block (1), and "Overhead" attacks require you to stand block (4), and, if you try to block these the wrong way, you'll just get hit. Most attacks are neither lows nor overheads, though, and you can block those either way.

The four attack buttons are light/heavy punch/kick. Here's the notation everybody uses:
A = Light Punch
B = Light Kick
C = Heavy Punch
D = Heavy Kick

Every character has these four attacks while standing, crouching, or jumping. Additionally, while standing or jumping, you can press C + D to get a special "Blowback" attack. Combine all these, and you have the 14 "Normals." Every character in the game has these 14 Normals, although the speeds and ranges and properties of these attacks might change from character to character.

Most standing Normals will change if you get really close to the opponent, called "close" Normals, or "proximity" Normals.

You can press A + B to do an invincible roll, and you can even roll backwards by pressing the buttons while holding backwards (4). Rolls are invincible to striking attacks and projectiles, but not to throws. Also, the tail end of the animation is not invincible to anything, so the opponent can react to your roll and do a quick attack to punish it, if they're in range and paying attention. Also, if you get knocked into the air by the opponent's attack, you can roll as you touch the ground to get up faster - this roll is completely invincible to everything for the entire animation, so it can't be punished at all, although it has one downside which I'll cover later.

If you're near the opponent, you can hold left or right and press a heavy attack button to throw them. The direction you hold doesn't matter, but the button you press does. Pressing C will throw them forward, and pressing D will throw them backwards. You have to be very, very, very, very close to the opponent in order for this to work - if you're out of range, of if they're not throwable for some reason, then you'll just get one of your Normal attacks instead. Throws are very fast and UNBLOCKABLE, so, if the opponent is just blocking everything, this is your simplest answer. The main weakness of throws is their incredibly short range.

Every character has "Command" attacks which are unique to the character and can be found in the pause menu's Command List. There's a page for Command Normals, Specials, Supers, Climaxes, and Throws. I'll get into the specifics of these attacks soon.

You can rapidly chain certain attacks into each other. This sounds complicated at first, but you just need to input two or more attacks in sequence - more specifically, you need to input the second attack right as the first attack connects, and the recovery of the first attack will be skipped, and the startup of the second attack will begin immediately. You can read more about Frame Data here:
https://docs.google.com/document/d/1tfSRTxgFy3A3WAbVQVTAOEKhfAYT7CO6WXE7yYDcunM/edit?usp=sharing

You can't just chain any attack into any other attack, though. There is a basic hierarchy you have to follow. First of all, certain LIGHT Normals, your A and B Normals, can chain into each other infinitely, although the opponent will eventually get pushed out of range after three or four of them. Secondly, you can chain up this ladder:
Normals > Command Normals > Specials > Supers

...with exceptions. Also, within your supers, you can chain up this ladder:
Lv1 Super > Lv2 Super > Lv3 Super

...and you can skip any levels in between. So you could even cancel a Normal into a Lv3 Super... but that's usually not recommended. Usually.

Uh, it's called "Power Meter." Another acceptable term is "Stick of Butter."

At the beginning of the match, you have 0 Power. You build more of it by striking the opponent, and by the opponent striking you, and by performing non-projectile special moves. It builds up to a certain maximum, and is spent to perform various new moves. You do not build Power for using or landing moves that cost Power.

Your first character can build up to a maximum of 300% Power. Your second character can build up to 400%, and your last up to 500%. You automatically gain 100% Power upon losing a round.

If you block an attack at the last second, right before it connects with you, you build additional Power and flash white. If you do this often, you build over double the Power of the opponent. Thus, projectile spam is not a very solid strategy.

EX Special Moves are performed by inputting a special move with two buttons instead of one, and cost 50% Power. The exact benefits of doing one of these is dependent on the character and move.

Guard Cancels are performed by pressing either Roll (A + B) or Blowback (C + D) while blocking, at the cost of 100% Power, and the Roll variant can be done in either direction. The properties of each of these is drastically different from the non-guard-cancel versions.

Guard Cancel Rolls are completely safe and unpunishable until you recover. The most common use of these is to escape the corner and/or punish the opponent for predictably canceling a normal into a slow special move.

Guard Cancel Blowbacks are invincible on startup, punishable on block, and deal insignificant damage on hit. This is a more desperate option, since it works in more situations, but doesn't reward you with damage. The only way to block one of these is after a deep jump-in or a slow projectile, things with very little recovery.

Input quarter-circle-forward (236) + C + D to perform a Shatter Strike at the cost of 100% Power. If it hits, it builds back 50% Power. If it's blocked, you're probably going to be punished. The startup of the move is armored against strikes, but not instantly, so it cannot be used to beat meaties. It also just loses to throws completely. On hit, the opponent crumples to the ground, and you get a combo. The combo is actually better if you cancel into the Shatter Strike from a Normal. If used twice in a combo, it ends the combo instantly. The two main uses of this move are as a high-reward predictive anti-air, and in combos with the intent to stun the opponent.

Super moves are written in the Command List, and cost 100% Power. Most of them also have an EX version which costs 200%. Every character also has a CLIMAX Super, which costs 300%.

Pressing B + C enters MAX Mode at the cost of 200% Power. Later characters on your team have longer MAX Mode durations, with your third character having 1.5x the duration of the first. You can cancel into MAX Mode from *any* grounded Normal, including ones that aren't normally cancelable; however, doing so will have negative consequences, including halving the duration.

During MAX Mode, you do NOT build Power, you deal +25% Damage and +100% Chip Damage, and all of your cheaper Power-consuming options consume some of the remaining MAX Mode time instead of Power. Level 2 Supers and CLIMAX Supers still cost 100% Power, on top of the remaining MAX Mode duration. Quick Max does not get the bonus damage.

In general, MAX Mode isn't optimal damage, especially since the opponent gets to build a lot of Power from getting hit. However, you can activate MAX Mode from any Normal attack to get a combo. This lets you get combos from things that normally don't give high reward, such as some overheads and long-range pokes. It's also a good way to stun the opponent in conjunction with Shatter Strike, for certain characters.

Throws
https://docs.google.com/document/d/1Jyh-mHq_hxQugfsmsnPKebkTvqKlmbAi2bb1G9EL0cQ/edit?usp=sharing

Standing Blowback
https://docs.google.com/document/d/1WhA8oH06Mq1_jJAOqU75Eza3OplgpNCNhJhkBu93p-E/edit?usp=sharing

Juggles
https://youtu.be/5ZMk_bIFvv0?list=PLx4aHLMyVhYq4oPaDwwzABUkrEHCxmG8-

Counter Hits
https://docs.google.com/document/d/1DfeLzmhKtSNuCRzxnev5owb7F8Mytdg8hNaaERryPpE/edit?usp=sharing

Input Tricks
https://youtu.be/ySIOKnenLK8?list=PLx4aHLMyVhYq4oPaDwwzABUkrEHCxmG8-

Skip, hop, jump!

https://youtu.be/TBK_RxMzXls

Punch! Block! Kick!

https://youtu.be/PyY9nhhaIpY

https://docs.google.com/document/d/1ouGB2QcLsEGiWVhyDXs6AdmvXZGs12c69CT8UD98k-s/edit?usp=sharing