In order to redeem a PSN key you can do it both Online and through your console.
If you chose to activate the key through Playstation website then sign in to your account.
Then click on your username and select “Redeem code” from the dropdown menu.
- Then paste your code in the designated area and redeem your code.
- If you chose to activate the key through your console then sign in to your PSN account.
- Go to the store page and go down to the bottom of the menu on the left.
Then click on “Redeem codes” and follow the steps to redeem your code