[zoombini]

Your not restricted to just your xbox either, you can use a memory card to take your gamertag account details with you & use them on another xbox.

But it basically works by plugging the ethernet cable into the back, setting the account up on the box & playing.
You may need a credit card to confirm your age etc before you can finalise the accoount. Choose your gamertag well.

Once setup, you start the games, go to multiplayer, select xbox live,
select quick start (= quickly chooses a game for you) where you go into the "lobby" (which is a waiting area that allows you to configure your play) before you get to start.
You have a mic/headset that allows you to chat to everyone else. Mostly you can just talk, on Ghost Recon you have too push the white button to talk.

You'll figure it out, if you dont we are here...