Are you referring to playing online?
There is a 2v2 Team setting on X-Box Live.
If you want to play just with some friends on 1 X-Box, just go to "Options" and set it up for "team" match. I forget the exact steps you need to do, but I think it's pretty simple.
If that doesn't work, just go to the "Settings" from the menu screen and go to "Game Types". From there you can create new game types and you can make one of them a "Team" game.
If you're playing online (X-Box Live or X-Box Connect), look me up:
my Gamertag for both is: