I wasn't trying to accuse you, only to point out how to ask questions effectively. You seem to be at the start of all this, so I'm trying to help.

From what you have said so far you have two problems:

1 How to get the program to behave correctly

2 How to create a new, unique game.

Both these are large topics. There's a lot that could be said and probably has been. So I'd suggest a number of things.

In reverse order:
2: is going to be difficult. To be completely original is hard. I'd suggest you start with a game you enjoy, find interesting enough to program, but simple enough to make some progress. Then change some aspects of it (setting, characters, goals) to make it more original, and to cut through to the essential simplicity of the game. If this is for a class, originality is unlikely to be the main goal, and programming is. But you can still be creative. There's years of games history to draw from. Pacman, Space Invaders, asteroids, ... As to what makes a good game, there's a lot written about that, but you have to keep the player interested.

1: is a big question, and has been the most annoying thing in the software industry for years. To distill my experience into a few short sentences, I'd say that to be sure the program works, you need to be sure what it should do. Then you need to break the problem down into surprisingly small chunks. As a programmer, you won't believe the stupid mistakes your brain can make for you. (Yes, I am speaking for myself!) So keep the components small and simple, and therefore easy to test. You must be sure what each one is to do, so you can test it. Then build bigger things out of collections of smaller things. In Alice the things will be methods most of the time. You can always make several world methods to test individual things, and change which one is run when you press play. That way you can test different ideas on their own. Also, even the best documentation cannot tell you everything you'd want to know, so a lot of programming is about experimentation. Try things to see if they work how you expect.

Proceed in small steps, because when they work they are encouraging, and when they don't they are small enough to fix.

Now, did I answer the question you were really asking, or did you mean something else?