src : contains the .java source files for your project.
gen : contains the .R file, a compiler-generated file that references all the resources found in your project.
bin : contains the Android package files .apk built by the ADT during the build process and everything else needed to run an Android application.
res/drawable-hdpi : this is a directory for drawable objects that are designed for high-density screens.
res/layout : this is a directory for files that define your app’s user interface.
res/values : this is a directory for other various XML files that contain a collection of resources, such as strings and colors definitions.
AndroidManifest.xml : this is the manifest file which describes the fundamental characteristics of the app and defines each of its components.
