First of all make sure you have an alpha key. If you already registered correctly you need to delete the 0's and put your username make sure you put the right password otherwise it seems to cause the 0 username bug. Otherwise, you shouldn't have a problem at all getting in. If you do need to register however you put your username and desired password and hit register it will prompt you for your key just copy and paste it from your email then use the username and password to log into the game. It might take a while to log in on the first go (if it is your first) sometimes if you close the game after registering and open it and log in it will go faster.