What goes into making an Android application?   Java for the computing.  Pictures, Icons and other resources for the eye/ear candy. A place to put all your button and title labels for easy language translation.  And a bunch of  XML to bind it all together.

The granddaddy of the binding files is “AndroidManifest.xml”

AndroidManifest.xml is the connector between the xml resource files and java programming.   For example. If you create a new screen(Activity) called “about”.  You will define the screen layout in the res/layout/about.xml file.   You will also create a new activity called  AboutActivity.java.  If tried to run it before updating the manifest,  the about screen would not be available.   Remember to add a new activity called .AboutActivity under the Application tab of the manifiest editor.