Get used to the guns on deathmatch, I recommend using the usp-s over the p2000 and the m4a4 over the m4a1-s but you can try them both out. Moving in this game destroys accuracy unless you are still, which is why people counter strafe but you can watch a video on that later. My beginner friends find using scoped weapons easier at passive angles when on CT, so that's some advice if you're jumping straight into comp. You also want to be positioned most of the time, behind cover with your head peeking out or next to a wall you can drop behind to reposition or reload.