<p>Area a like top level site. Topic, news, sites are three area created by default. They share the same feature that area has. An area has three default components(portal lists, document library, and image library). Topic has shortcut to create subarea. Topic area does not use any of this component. News use portal lists to add news. Sites area does not use default component. Instead it add one more custom lists(the name is Sites). Sites area has a shortcut to create site, in the process of site creation, you can add the short cut this site. This shortcut is actually an record in the "Sites" custome list.
The root area is home. Topic, news, sites area are all </p>