AndroidManifest.xml: An XML file describing the application being
built and which components—activities, services, and so on—are
being supplied by that application.
bulid.xml: An Ant script for compiling the application and installing it
on the device.
defalt.properties and local.properties: Property files used by the
Ant build script.
asset: A folder that holds other static files you wish packaged with
the application for deployment onto the device.
bin: A folder that holds the application once it is compiled.
gen: Where Android’s build tools will place source code that they
generate.
libs: A folder that holds any third-party JARs your application
requires.
src: A folder that holds the Java source code for the application.
res: A folder that holds resources—such as icons, graphic user
interface (GUI) layouts, and the like—that are packaged with the
compiled Java in the application.
tests: A folder that holds an entirely separate Android project used
for testing the one you created.
res/drawable: For images (PNG, JPEG, etc.).
res/layout: For XML-based UI layout specifications.
res/menu: For XML-based menu specifications.
res/raw: For general-purpose files (e.g., a CSV file of account
information).
res/value: For strings, dimensions, and the like.
res/xml: For other general-purpose XML files you wish to ship.