Select the constant controller at bottom left and change the value of the constant, a, and observe the transformations.
Also if you select OPTIONS and choose animation up/down and set values say -5 to 5, steps 0.1, or 1 (to speed it up) click ok and press play. Enjoy!

If you make any errors, start again! You can use the pen in class discussions.
You may need to download Autograph Player (Link at bottom of this page).