Whenever we create an android app we have many folders in out solution which are used for building application in android.

Drawable folder in android app is mainly used to change or set the background image of an android application .In that folder we have different sub folders

1. drawable-ldpi
2. drawable-mdpi
3. drawable-hdpi
4. drawable-xhdpi




These four folders are mainly used to store the images want to set in our application.

Low density            ldpi    
Medium density         mdpi   
High density           hdpi 
Extra High density    xhdpi

We can simply set the image

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layoutwidth="fillparent"
    android:layoutheight="fillparent"
    android:background="@drawable/myimage">