I have never played it before, and i didn't read anything on it online. i just seen previews for it and thought it looked really fun. Can you play it without having to play it online?

The actual point of the game is that every person in it is guided by a real person. There are no drones or AI, and you are one of eight people in a squad.
http://en.wikipedia.org/wiki/MAG_%28video_game%29

Check out this thread for a little bit of discussion on the game:
http://forum.dvdtalk.com/video-game-...e-playing.html

There's no single-player campaign, but I think there's one single-player mission, which is just a tutorial really.

I love the game, myself. Completing actual objectives is pretty satisfying.