Your Stardock.net account is used here by the forums, in Stardock Central, on other Stardock sites, and also to manage your Metaverse characters. "One account to rule them all."
Your account can have up to THREE characters tied to it. Most people will have only 1 but this way, if you have multiple people in your family playing the game (my son plays for instance) they can use a character.
If you've already pre-loaded, you should be able to go to the Metaverse and Manager Characters. You will need your serial # to create another character.
If you have any problems, let us know.