There are three demo usernames available with which you may try out this site.
demo1
An administrative user. This user can change the theme, create all types of content, and change the site's title, among other things. While some functions are disabled in this demo, this is the role that most closely resembles the experience of a site owner.
demo2
demo3
An authenticated user. Not required by all sites, but on a site that makes special features available to registered users, any user that registers with the site will be assigned this role.