PSN Activation Procedure
1. Turn on your PS4. Don't log in to your own account, but create a "new user" with the data you have received via eMail.
Note: Log in to the account ONLY on your PS4 console, NOT via your PC!
2. When the new user was created, go to "Settings".
3. Go to PSN/Account Management.
4. Choose "Activate as Your Primary PS4".
5. Click on "Activate". This enables all the users on your Playstation 4 to use the contents that are downloaded with this account.
6. After that, go to your games and apps library (at the far right in the home screen).
7. There you can see your new game (here: BATMAN ARKHAM KNIGHT) besides the games you already have on your Playstation 4. Choose the new game.
8. Here you can start the download for the game (and, if available, the download for associated DLCs).
9. Just after starting the download, switch back to your own account. Go to "Power", then on "Switch User" and choose your own personal account.
10. When the download of the game (and possible DLCs) is complete, it is available to you using your personal PSN account. You can start and play the PS4 game now as usual. Have fun!