In order to get your free Steam key, you need to
- Login, or register a new account, at http://www.dlh.net
- Visit Steam Keys page (Profile > Steam Keys on tab menu)
- Scroll down to the "Pirates of Black Cove" giveaway, fulfil all requirements and get your Steam key. There are hourly/daily limits of available keys so if it's not working at the moment, you should try again later
The Steam key will appear on the same page. Enjoy!