it just takes a week or two to get it back man. you'll be a killing machine in no time. also, when you do go online, remember that the game puts you in a server based on your rank. if you join games w/ us you'll be up against higher ranking people and you'll get pwned at first. try joining matches then inviting us if you can. that way you'll be playing against lower ranks and you won't get beat up as much.

and like red said, fire in bursts if your gonna use a machine gun. full auto will just spray all over the place.
I would just stick w/ either the assault or medic class at first if I were you. those two classes allow you to rack up a lot of points fast by using the med packs and ammo packs (which you'll have to unlock first).
just squad up w/ someone from here to learn the basics then start grinding points to unlock those packs and you'll be ranked up soon.