android folder

ProjectName 
ProjectName/src
e.g. R.java and <activity>.java (in this example,
HelloWorldText.java,developProgram.java ), The file R.java is an auto-generated file that is added to your application by the Android plugin. This file contains pointers into the drawable, layout, and values directories (or the items within the directories, as is the case with strings and icons). You should never have to modify this file directly.

/ProjectName/assets
audio files for streaming and animation assets
jpg, html, js,css

/ProjectName/res/drawable
imageFiles, drawable-hdpi, drawable-ldpi, drawable-mdpi3

/ProjectName/res/layout
 main.xml, layout, XML files

/ProjectName/res/values 
string.xml, color.xml, style.xml

e.g. main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android=http://schemas.android.com/apk/res/android
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Hello World, HelloWorldText"
/>
</LinearLayout>