Click the pinwheels to get them spinning. This is a simple demo.
UPDATED: It wasn't working because of a change to Scratch. You need to add an "When Green Flag Clicked" and "Forever Loop" with a "Wait 1 Secs" block so the program doesn't stop right after you click it.
See how this program is made at https://inventwithscratch.com/2013/08/20/pinwheel-demo/
Learn to program games with this free online Scratch course: https://inventwithscratch.com/class