Type the code in here. https://buy.itunes.apple.com/WebObjects/MZFinance.woa/wa/redeemLandingPage Edit: It can be found on the front page of iTunes in top right corner, the link that says redeem.
You can also redeem codes directly on your device via the App Store. Go to the "Featured" page and scroll to the bottom. You'll find a "Redeem" button in the middle. Type your code in there. If you use iTunes, you can redeem any code. If you redeem a code on your device, the code has to be for an app that is compatible with that device. For example, you can't redeem a code for an iPad game on your iPhone.
