src: 

This 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. You should not modify this file.

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.

src: 

This 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. You should not modify this file.

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.