Instructions
Pick up an Xbox Live membership card. They can be found for sale at most, if not all, games and electronics stores.
Hook up your Xbox 360 to an active internet connection. Your Xbox will need to have access to the internet for you to sign up for a gamer tag or for Xbox live.
Sign up for a gamer profile on Xbox Live. You will need to have a gamer profile to access Xbox Live and gain access to the marketplace. This can be accomplished under the “Xbox Live” tab under the Xbox 360 Dashboard. Once you are signed up for a gamer tag, you should be signed into it automatically. If you are not, hit the “sign in” button under the “Xbox Live” tab.
Highlight your gamer tag in the upper left portion of the screen and press the A button. This will bring you to another menu under your profile.
Select the “Account Management” option under your profile. Select the “Memberships” option in this menu. This will bring you to your current Xbox Live membership. It will be silver by default. Press the “A” button, and you will be presented with another menu. Select “Redeem code.”
Enter the code from the Xbox Live membership card you purchased. It will give you Access to Xbox Live Gold, which will allow you to play online multiplayer through Xbox Live. You will have a preset amount of time determined by the card that you purchased.