When you first enter the site (assuming you've logged into your Square Enix Member's account), you'll be greeted by a quiz that will determine your job (this blogger sadly conjured up the lamest of the lame jobs, the white mage). Once you have a job and a house, you can dally around the town.
Different places in the virtual kingdom let you do various things. At the castle, you can write questions, comments, or thoughts about the game to its developers. Throughout the town you can also check out the bulletin to see the "king's behests," download some goodies (like screen savers), see other members' "houses," and other random stuff.
The website is a nice idea for fan service, but to be honest, there's no reason to spend more than five minutes there at the moment. Hopefully Square Enix will add some more neat things to it soon.