With the credit from a gift card, you can get music, movies, TV shows, apps, books, audiobooks, Apple Music memberships, iCloud storage, and more.
When you redeem an App Store & iTunes Gift Card, the amount on the card credits to your Apple ID. You can use the credit in the iTunes Store, App Store, or iBooks Store as long as you sign in to each store with the same Apple ID. The credit is used for each purchase you make in a store until it’s gone.
How to Redeem iTunes Gift Card:
How to redeem iTunes gift cards on iPhone and iPad
1. Open iTunes Store, App Store or iBooks on your iOS device.
2. In iTunes Store, App Store or iBooks, tap the Featured tab, then scroll to the very bottom of the screen and tap the Redeem option.
How to redeem iTunes gifts card on Mac and Windows PCs
1. Open iTunes on your Mac or Windows PC.
2. Choose Music, Movies, TV Shows or Apps from the popup menu near the top-left corner, then click the Store tab near the top of the screen.
3. Click the Redeem link under the Quick Links heading on the right side