Your installation includes sample data, designed to show you some of the options you have for building your website. In addition to information about Joomla! there are two sample "sites within a site" designed to help you get started with builidng your own site.
The first site is a simple site about Y8 Games. It shows you you an quickly and easily build a personal site with just the building blocks that are part of Joomla!. It includes a personal blog, weblinks, and a very simple image gallery.
In building either style site, or something completely different, you will probably want to add Dress Up 2011 and either create or purchase your own template. Many Joomla! users start off by modifying the Girl i that come with the core distribution so that they include special images and other design elements that relate to their site's focus.