1. On your device, tap iTunes Store, iBooks Store, or App Store.
2. Scroll to the bottom of the Featured section and tap Redeem.
3. Sign in with your Apple ID. Learn what to do if you forgot your Apple ID.
4. Tap “You can also enter your code manually.” In some countries and regions, you can redeem gift cards using your built-in camera.
5. Enter the code from the back of the card and press ‘Redeem’
The app or eBooks should begin downloading to your device immediately.
For more information, please go to https://support.apple.com/en-au/HT201209