What is the purpose of "onFling" and "onScroll" event in GestureDetector of Android?

I am developing an Android application. I am novice in Touch enabled Android Application. I have read the article about onFling and onScroll events on:

http://de开发者_如何学Cveloper.android.com/reference/android/view/GestureDetector.OnGestureListener.html

But I didn't get exactly what is the meaning and for what we can use onFling and onScroll events.

onScroll event is when user touches down the screen, moves finger in some direction and lift up. It is mostly used to scroll larger layouts over a smaller viewport. onFling is the same, but made faster and usually triggers an animation that keeps scrolling few moments more after finger lifted up.