This is the Home page of your site.
More specifically it is the "Front page" of the first collection of your site. This first collection is called "Home". Several other sample collections may have been created during the setup process. You can access these collections by clicking "Blog A", "Blog B", "Photos", etc. in the menu bar at the top of this page.
You can think of collections as "sections" of your site. Different collections/sections may have different purposes: blog, photo gallery, forums, manual, etc. You can add or remove collections at will through the back-office. You can even remove this "Home" collection if you don't need it.
Feel free to experiment! If you delete all collections, the Quick start wizard will come back and you will be able to start with a completely new arrangement of collections.