When ever i create a new project, the Fragment_main.xml file is added to my Layout folder and unlike in Eclipse it is this file that contains what is normally in the Activit
The Activity_main.xml contains the Layout for the FragmentActivity and the fragment_main.xml is the Layout for the fragment.
For more information to fragments and how you can use it. Visit: http://developer.android.com/training/basics/fragments/index.html