1. Login to your PSN account
2. Under your account panel, click "Redeem Prepaid Card"
3. Enter your code and click "Continue"
4. Confirm your redemption "Redeem Item"
5. Redemption confirmation will be displayed on your screen
Playstation network
Activation guides for other platforms:
battlenet
bethesda
ea
epicgamesstore
gogcom
other
rockstar games
steam
ubisoft connect
xbox live