How do you limit the final movie to just the stage?

I know this may sound like a dumb question,but I’m a flash newbie so please be kind. I don’t want the things off the stage to show in my final movie, and I can’t figure out how to do that. I know I could mask it or something, but I don’t want the final window to have a big blank area around the stage. What should I do?

Thank you very much for any help you can give me.