As always, the smartest thing to do is to break down your goal into a smaller set of tasks and then go through the tutorials or helpfiles or example patches to find the things that relate to those tasks.

In your case, it looks like you'll want to do some kind of drawing using mouse position. That would mean having a look at the jit.lcd object, and probably having a look at the mousestate object. For keying, you would probably want to have a look at the jit.chromakey object or take a look at the Jitter tutorial on alpha channel blending.

But a lot of that will be difficult for you if you don't do the basic tutorials in order to understanding how Max does message passing, which is why nearly everyone will tell you to start with the basics (tutorials) - they're at the heart of nearly everything you'll be doing.

It's a very doable project. Good luck.

thanks a lot:)