Pythagoras Formula in Squeak Etoys

Bert posted a youtube video as a response to a newbie question:

For her third language she chose Squeak, since she knew that Scratch was written in it. I would like to have her write the “Hello Pythagoras” program using Morphic objects, in a visually appealing way. So far I have had some trouble finding a tutorial that covers relevant information. I am sure I can figure this out by poking around long enough but if anyone has a pointer to documentation that might help, or a similar example, that would be great and much appreciated

Here is Bert’s terrific answer!