In short, if you want to register the 12 digit code you got (which grants you 30 days) you need to do this:

1. Go to Account Management on your PS3.
2. Select Redeem Code.
3. Enter the 12 digit code (XXXX-XXXX-XXXX)
4. Then press continue until you reach the message "Thank you for using the Playstation Network" or something to that regard.
5. The next step is key. If you have the client downloaded, enter it and log in. You will be prompted to accept the agreement. Do so.
6. Check if everything you should be having is valid.
7. If you want to continue to use the characters and the benefits from Phase 4/Early Access onwards, do NOT click to create a new service account. Just click "Next" under it.
8. It should say you are registering the PS3 version of the game.
9. Finish the process and voila - 30 days registered.