What determines your home page?
From Joomla! Documentation
Your "home" page in a traditional HTML site--the page that shows when you type mydomain.com for example--is the page in the index.html file.
Joomla! is a database-driven content management system (CMS); it does not have HTML pages, but rather assembles the pages from the MySQL database.
When you install Joomla! by default it has a menu link to the frontpage component as the home page. However, any content, component or other link can be used as the home page.
Changing the Home Page[edit]
The "page" that shows is determined by the Main Menu. Go to Menu > Main Menu. Select the item you would like as the home page and click the default icon.