Economy 101:
You get $1400 for losing, $1900 for next round if you lose again, $2400 if you lose yet again, ... etc., maximum loses is $3400. You get $3250 for winning.
Those are the minimum so you can guarantee those numbers every round. New players like yourself shouldn't get distracted by kill bonuses and 10 million other things yet. For now use basic math to get to:
- $4000 playing as Terrorist: buy AK47 and full armor. Buy grenades with the rest if you like, but again, new player like yourself should focus on aiming first.
- $4500 playing as Counter-Terrorist: buy M4, full armor and defuse kit.

Grenades: you should learn to throw grenade after spending some time with the game. Those utilities won't be used much when you go against new players like yourself anyway. Focus on flashbangs as they will blind your enemy giving you a better chance to kill them.

Which place: Where there is an angle, a corner, any place where the opponents have to turn around before shooting you, but you only need to click to shoot them.

Mute:
1. hold TAB, then right click once to see your cursor
2. right click on the player's name on the board
3.click mute.

(This is very basic, so basic that in 2 months you can come back and see that these advises can only be true during your first month playing, and will become increasingly wrong when you get to learn new stuff)