Use an Apple Gift Card in iTunes on PC
If you receive an Apple Gift Card, iTunes Store Gift Card, or promotional code, you can use it to buy songs, videos, or audiobooks from the iTunes Store.
Note: Gift cards are only valid in the country or region in which they’re purchased.
In the iTunes app on your PC, sign in to the iTunes Store if you’re not already signed in.
Choose Account > Redeem, then follow the onscreen instructions.
You don’t need to enter credit card information to redeem only the amount of a gift card.
Your balance appears in the top-right corner of the Store window.