Download and install iTunes, if you do not already have the program. Downloading iTunes is free. Visit the official iTunes website (http://www.apple.com/itunes) to download the program.
Register for your iTunes account. You need a valid email address to register. Run the iTunes program, and click on "Store>Create Account" to register. If you are already registered, sign into your account.
Access the iTunes Store. Once you are signed in, you can access the iTunes Store by clicking "iTunes Store" on the left side of the program.
Scratch off the gray strip (using a coin) on the back of your iTunes gift card; this will reveal a 16-digit code.
Click on "Redeem" on the right side of the iTunes store interface. Enter the 16-digit code from your iTunes card; click on "Redeem" again to add the card to your profile.
The money on the card will be transferred to your iTunes account; any purchases you make will be deducted from your account balance.