When you create new android project from eclipse editor you found that there are lots of directories created for android application lets us understand all these directory.
Let us start from the top directory the top most directory is src directory.
The src Directory contains the java files inside package.
The gen directory contains folder that are generated for us by the toolset. one of the best thing you will find in gen directory is R.java file. R.java file update automatically by the system whenever you add or remove the design object or anything. in straight forward way whatever you add or remove from your project will be update in R.java file.
Android 1.5 or X.X
This folder is associate with the SDK version this is the thing that we have to configure when we create new project of android application.
the assets folder provides repository for your resource which are using by your android application. for eg if your android application has sound effect then you can put those sound files in this folder but you can't put image files in this folder because we have another folder for images like stuff.
Every program gets compiled and generate binary files same way android program also gets compiled and generate binary files. android bin folder contains the compiled binary files.
the res folder doesn't contain any files but it is one of the most important directory in android application. let us see what kind of directory res folder has.
Drawable folder contains images. there are three kind of screen density. you can specify same three images for different screen density. for eg res/drawable-hdpi contains all your image resources for high-resolution devices. you don't need to specify which density images to pick when but operating system will choose it at run time.
the layout folder is where you put your main.xml file. all design resources are stored in this folder.
values folder contains string resource. mostly its in key value pair. some common file is strings.xml
The manifest file is responsible for providing essential information to the operating system about a particular application. for e.g. used to specify the default activity to launch.