Instructions
Power on your Xbox 360 without a disc in the drive and log into your Xbox Live account.
Scroll down to "Friends" on the Xbox 360 profile dashboard and select it. This will bring up a list of your friends organized by their gamertags.
Click the "Add Friend" option and you&'ll be prompted to enter a gamertag.
Enter your friend&'s gamertag into the onscreen keyboard exactly as it appears, taking capitalization into account. When finished, click "Done."
Click "Send Friend Request" on the following screen. Once your friend has accepted, you&'ll be able to set up matches and be alerted to whenever either of you is online.