An autoconfirmed user is simply a user who has had an account for more than a few days. As the user class name implies, this is an entirely automatic action, performed by the wiki software itself. Autoconfirmed users have all of the rights that regular users have, and are additionally allowed to edit semi-protected pages, like the WotLK content portal. See Special:ListGroupRights for a full list of permissions users/autoconfirmed users have.