To activate on your Mac:
1. Open the App Store and go to account settings.
2. Click "Redeem Gift Card".
3. Enter the purchased code
To activate on your iPhone, iPod touch or iPad:
App Store:
1. Go to the App Store.
2. Go to the "Settings (upper right corner)" section and go to Redeem Gift Card or Code.
3. Click "Activate with code".
4. Enter the purchased code
iTunes:
1. Go to the iTunes store.
2. Go to the "Music" section and go to the end of the section.
3. Click "Activate".
4. Enter the purchased code