All you need to do is head over to our giveaway page to pick up a key. Then go to Drakensang Online's main page, click "play now for free" to register, and enter your key in the field at the bottom of the registration window.
Drakensang Online is browser-based, so once you're registered, you're free to jump right in and start playing!
[Update: The techies for our giveaway page have let us know that there was an IP tracking issue with one of the servers. The problem has been fixed, and keys will now be distributed correctly. We've raised the IP lock for now, so even if you got a key before, you're clear to claim another one. Thanks for your patience!]