It's been a couple of weeks since you first posted, so you're probably a SF sergeant by now! If you still haven't taken the online plunge, try exploring an easy map offline first to get the hang of it, then go online. I suggest you start with the easiest map to play, Bridge Crossing, and take the defense side so you can just camp and let the action come to you.
Since you're a complete newbie, follow these instructions to start an offline Bridge Crossing map:
When the first screen comes up after loading the game, hit the ~ key. This will bring up the console where you can enter commands to load a game. Type (without the quotes for any of these instructions) "start bridge" and hit return. After the bridge map loads hit the ~ again and type "mpcheat changeclass r" and hit return again, which put your handy dandy AR in your sweaty palms. Then type "playerlock 0" and hit return, so you can move around. Hit the ~ key again to get the console out of your way. You'll be starting from the assault side of the bridge so cross to the other end and explore all the places where you can take cover and fire from. When you have a feel for it, join an online Bridge game and just follow the crowd for a while till you get the hang of it. Learn the simple commands for reporting in "u", and team talk "y" so you can appologize for shooting someone on your side (called a TK for Team Kill).
Hope this helps newbie's take the plunge. Yes, the adrenalin can really flow as if real bullets are flying past your noggin!