PlayStation gift cards are prepaid cards with a pre-determined balance and are used to add funds to your PlayStation account. Once funds have been added, they can be used to purchase games and other products from the PlayStation Store.
When you purchase a PlayStation card you need to log in to your PlayStation account and redeem it to add the balance to your wallet.
To redeem a PlayStation gift card, turn on the console and log in to your PlayStation Network (PSN) account. Then go to the PlayStation Store and look for the "Redeem Codes" option. Here you will be able to enter the card code and the balance will be automatically added to your PlayStation account.
Once you have added the balance to your wallet you can use it to buy games and other products from the official store.