To redeem a code from Google Play, first copy the code from the box. Then launch the Play Store app on your device, and tap the hamburger menu in the search bar.
Scroll down and tap Redeem. Paste your code and tap Redeem.
To redeem a code from the Apple App Store, first copy the code from the box. Then launch the iTunes app on your device, and scroll to the bottom of the Featured section.
Tap You can also enter your code manually and paste your code. Sign in with your Apple ID to download the app.