Playing online against other players can be daunting, especially if this is your first Tekken. You don't know your own character's moves, and you don't know the opponent character's moves. This makes the matches feel chaotic and overwhelming...

I'm going to assume you are a new player battling against other other low level players, and provide you with some useful tips that will provide you some breathing room during the match so you can learn the game at ease.

1. Almost always defend high- If you see that slow, telegraphed sweep coming your way, then react accordingly and block it low, but the rest of the time always defend high and let the quick, unpredictable lows hit you. You'll end up taking way less damage compared to crouching against mids. It's all about applying logical risk-reward when you are facing unknown patterns of attack.

2. Utilize your backdash- Even if you don't know how to perform sophisticated high level movement, the simple singular backdash is still a powerful tool. Based on tip #1, you are already blocking high right? A backdash allows you to move backwards while still maintaining a high block all the way. This creates breathing space safely and may even cause the opponent to whiff moves.

3. Jabs are your best friends- Jabs are the fastest moves in the game, and this speed gives them many roles. Pressure tools, panic buttons, -10f punishers... Low level players like going for big, slower moves and don't try to understand who is at the frame advantage and when. Quick jab strings tend to hit them a lot because of this, and the damage adds up quickly. In addition, most 2 hit jab strings are not punishable on block, which allows you to try to retaliate after blocking every move you don't know. If it's jab punishable, you get free damage. If it's safe, then your punish attempt is safe as well. This way you can slowly learn which moves in the game are punishable on block without taking needless risks yourself.

Check your character's frame data and look for all the entries that have 10 frame startup, and are less than -10 on block. All of these are your candidates for a jab string of choice.
http://rbnorway.org/T7-frame-data/

4. Don't always rush to get up from the ground- The opponent doesn't have many moves that can hit you on the ground, and if they do, the damage is usually minimal, and pushes you away which then allows you to get up safely. Many times the opponent will whiff a move above you, which you can easily punish with a wakeup kick, or at least use that time to get up normally by pressing "up", which is usually the safest way to get up from the ground anyway. (Pressing "up" then blocking high.)

5. Always expect the "Hail Mary"- Give a low level player Rage and you just know the Rage Art will be thrown at you eventually. As soon as Rage enters play, start playing extremely defensively. Only use moves that will kill on the next hit, through the super armor of the Rage Art, or moves that recover extremely quickly like a single jab.

6. Learn to do a basic juggle from one of your fast launchers- Juggles are a big part of Tekken, so at least learn to do a one easy, basic juggle. A basic juggle can consist of an initial move, then a "screw" move, then a finisher move. If a juggle is too hard, try to omit one of the hits, until you find something that's easy enough to do which still inflicts more than 40 damage. Use the waiting room in the quick match search to practice it between matches. You need it to make your opponents pay for their stupid mistakes, such as getting their Rage Art blocked.

7. Find a simple wall ender- Since you are already learning a juggle, you need to be prepared for all the times the opponent gets splattered on a wall. An easy to use wall ender would be a big single hit that's quick to come out, like Paul's Death Fist. It's also the most consistent type of wall ender, that will work in weird angles as well.

This videos shows the concepts of a basic juggle and a basic wall ender
https://www.youtube.com/watch?v=JSPAq4IWSNI

8. If this wasn't clear yet, don't gamble with your Rage Arts- Don't be tempted by the flashy animation and the big damage. Without the proper knowledge Rage Arts will hurt you more than benefit you, because they are highly punishable on block. Rage Drives are also out of the question as they have tactical uses which are not obvious at lower levels of play. Just enjoy the extra damage the Rage Art gives you, or use it to punish big moves (or blocked Rage Arts) instead of a launcher.

9. Are people still using those silly 10 hit strings? They only work for the first couple of times. Once you know when the first low hit comes you can just low parry it and get your free damage. Please note that a very small minority of 10 hit strings are actually useful at high level play, but only their initial hits, not the full strings.
https://www.youtube.com/watch?v=BtH1sonZ3TE

10. Now that you have all the tools you need to provide you breathing room, check out the top 15 movelist of your character and start exploring the moves one by one as you play.
https://drunkardshade.com/2017/05/27/tekken-7-top-15-moves-for-all-characters/

And if all else fails, you can always ask for help on the Tekken Zaibatsu Discord server. https://discord.gg/C6EG5gA

Good luck online!