Thanks Metalucas, yes you can tell here where you are blocked on the tutorial, you define the function playSquare in the chapter 4. I have not built this tutorial so much thinking about how to do test along the way, you won't be able to try the game before you defined all the functions.
I found than the easiest way to explore the code is to compare the complete project than you can download here and launch in superpowers with your own program, it is a nice way to do tests with your own and check the original in the same time. If you found out an error in the tutorial you can tell me and I will change it.
For the explanations of the Superpowers functions, I am thinking about a little guide for the tutorials to refer to.