When the app starts, press to move over to ‘Library’ and select ‘Interactive Episodes’.
This is unlocked in Episode 1, ‘Elmozilla’, Chapter 1, ‘Play Catch with Elmo’.
When Elmo is on the farm, just move your arm in a throwing motion to throw the ball to Elmo. Do this each time he tells you to throw the ball.
The simplest way to unlock this achievement is using ‘Chapter Select’ to choose the chapter. When the chapter is over and the next one starts, just press , move over to ‘Stop’ and press again. The achievement will unlock when it is buffering. You can alternatively watch the entire episode, but that would be more time consuming.