Just made.an bnet account, I need bnet balance or smthg else ?

you only need subscription or game time.

https://eu.shop.battle.net/en-gb/product/world-of-warcraft-game-time

or

https://eu.shop.battle.net/en-gb/product/world-of-warcraft-game-time

game time has same price, except when it expires you will have to renew manually, subscription takes money from your cc by itself.

So i need to trade fg for gametime gift ?

no, you can get tokens if you want to pay with fg.

Can i use token without bfa and an active sub ?

no u need active sub to use token, u can buy token with ingame gold if your accumulated gold on one server adds up to the current cost of a token though.
If not your paying money for your first month first.