How to redeem promotional code, iTunes Gift Card, or iTunes Gift Certificate

There are several types of codes that can be redeemed on the iTunes Store, including promotional codes, iTunes Gift Cards, and iTunes Gift Certificates. Just follow the simple steps outlined in this Apple's Support article: http://support.apple.com/kb/HT1574

For complete list of App Store and iTunes related articles see: http://www.apple.com/support/itunes/