Once the app is created, follow the onboarding steps to create your bitcoin/litecoin address.
Click Menu -> Settings -> Import Wallet.
Scan the QR code on your gift card with the app.
Voila, you should have redeemed your gift card. You can now use your wallet to send and receive bitcoin/litecoin.
* Skip steps 1-2 if you have a mobile bitcoin/litecoin wallet capable of importing cryptocurrency with a QR code (most mobile wallets do)