What is happening right now?

You create a Car object, but show a cars class. Cannot do anything about the counter until it is known what you are doing there. Remove act(); from the Level2 class constructor and then take the first 3 lines in act and move them to the prepare method.

Please refer to my Scrolling Tutorial scenario. It does not specifically cover mouse-at-edge action, but other than that, it will not be any different.

Starting off with a big game is probably not the best idea. I'd recommend you to start with the basics of Java, and then slowly start making bigger and bigger projects. But a game already is not a good start I think