And... that's where the pong chapter ends. Amethyst is still in development and writing good tutorials is hard, so the guide is not complete yet. We are sorry this might feel a bit disappointing.
Fortunately, the pong example is complete, and you can find the entire code with balls, score and music on the example pages available here.
We hate to have an incomplete tutorial as much as you do, and you can help us complete it! As stated above, the code is ready, tested and working. If you have some experience with the engine and you know how to write a tutorial, you can reach us out and we will help you do it by giving you details on how things work and how to structure it.
Feel free to ping us on Discord or in a GitHub issue!