There is a large choice, but the nations are the best in terms of technology: Germany, USSR, Italy, China, Sweden, Israel (opens at rank 4, and does not open in some countries, for example: Germany, etc., which do not support Israel real time), USA

Well, you have 4 choices, helicopters are unlocked after receiving rank 5 and above.
Contents of some countries: Airplanes, tanks, navy, helicopters.
Some countries don’t have a fleet, so let’s get to the point.
Are you wondering what equipment to download? Have you decided to upgrade your fleet or aviation first? Is it worth it?
You need to upgrade your ground vehicles, since you will still have to switch to the ground.
Explanations: you may get bored playing in aviation or navy, well, whoever has pumped up their nerves to level 1,000,000, well, you're lucky!

Aviation, navy, etc., have their own type of projectile, and if you hover the cursor over the ammunition, you can see the armor penetration from below, the greater it is, the greater the chance of making a frag - kill, bullets also have penetration, and you can see the caliber - armor penetration depends on it.
The best shells for tanks
Land mine - destroys tanks with an open wheelhouse and light protection (small caliber does not work on tanks of a higher level), the larger the caliber of the land mine, the greater the chance of humiliating the enemy crew
Armor-piercing projectile - penetrates the tank and explodes inside.
OBPS is a very good projectile, it works like a laser, it penetrates through, the greater the penetration, the greater the chance of penetration from any angle.
A cumulative non-rotating projectile works almost like an OBPS but not through and through, and everything again depends on the caliber and armor penetration.
High Explosive Armor Piercing Projectile - (I'm not really sure), but in my opinion it works very well against armored plate tanks.
For ZSU calibers 15-20-30-40-50... mm it is better to use BTZ.
For low-rank aviation (1.0-4.3) it is better to use anti-aircraft; for aviation br 4.7-12.3 it is better to use BTZ if possible.
Well, from the fleet, you yourself will understand what’s what.

About different features
Radar - opens at ranks 5 - 6 (on SPAA vehicles, aviation, navy, helicopters.)
NVG - opens at rank 4 - 5 (on land, aviation, navy - not a fact, helicopters)
Thermal imager - opens at rank 6 and rarely at rank 5 and usually on premium vehicles (ground, aviation, helicopters)

Missiles on helicopters and planes and tanks. See missile control in settings or in controls (F1)
URVV - Guided air-to-air missile, against aircraft (auto-aiming).
URVP - Air-to-surface guided missile, anti-ground (manual aiming).
Unguided missile - (launch starts from the left, then from the right, aim more carefully)
ATGM - anti-tank guided missile (targeted).
Bombs - only helicopters have this. and aviation. (Aim at the sight from below. IMPORTANT! Reset until fully aimed, they reset with a delay).

There are 2 game currencies:
Golden eagles and silver lions
Golden eagles are an expensive currency, you can get them in these ways: buy on the website, receive through a promotional code, participate in various quizzes and so on, in the chest, during training - a one-time payment.
Silver lions are a common currency, can be obtained: at the end of the round, in a chest, bought on the website, completing tasks, at the training ground they will not give rewards by completing a bet (they are available from rank III!)
Well, this is all about currencies, now RP is research points.
There are 3 types: free, combat and regimental
You can only get a combat one at the end of the round, and that’s it!
Regimental one can only be obtained in a regiment for activity, and after 3 days, experience will be given out every 3 days.
Free will be given at the end of the round, and for completing tasks.
Where to use free experience? - You ask, it can be converted into researchable equipment and modules, their conversion costs gold, I do not advise you to immediately spend money on conversion.
Where to use combat experience? - It’s very simple, combat experience is awarded to researched equipment and modules, when the maximum is reached, then you can buy modules or equipment for silver, the higher the rank, the more expensive.
Where to use regimental experience? - Good question, it can be spent on regimental equipment which is in the premium tanks/helicopters/navy/aviation section, and equipment with a green background. And you can buy regimental equipment either through gold coins, or you can download regimental glasses for a long time in order to buy it for a small amount, in my case the M901. 500,000 silver and training 130,000 silver.

I did this from my own experience, I hope you will appreciate it with awards and likes, at the time of writing this text we had 1:55 make this guide popular.
I will update the guide occasionally.
The best advice is - don't start playing, don't make a mistake! Otherwise it will be worse!(Not a threat)