The AK47 / M4A4 are the two weapons you should buy when you have enough money. These are your bread and butter rifles, so to speak. You only buy a P90 when you can't afford these. Also, buy an AWP if you want to and have enough money, it's more of a choice than anything. If you're good at it, do it, if not, run away. At higher levels it is frowned upon to buy an auto sniper, and if you're against a good AWPer, you'll get destroyed. Oh, and, NEVER buy guns without buying armour, always check to see if you can buy armour too.
1000+ hours in csgo here, not a silver 3 *looks at exrobite*
For eco rounds, its best to buy a cz or a p250, because these are very good against armour, and if you can get 1 kill with them you have made your money back, for anti eco rounds, its best to go with a cheap gun like a smg or a shotgun to get lots o money of kills, but be wary of suprise head armour buys, where your anus will be penetrated because you do little damage, for buy rounds, always go with the ak/m4, m4a1-s is better if you are with someone else on a site, because you dont need that extra ammo, and if you buy an awp, it needs to be a big investment, so dont die straight away, because you need to make it pay off rounds wise, whenever its not an eco, buy as many nades as you can, and make sure to use your money on pistol round, because you have it for a reason
well
if you are a CT, kill the Ts
if you are a T, kill the CTs
aim at them, left click
sometimes you kill them, sometimes not
sometimes they shoot back, sometimes not.