If by "get the gamecube files" you mean to download them, then you're probably going to get banned, or at least get a warning. READ THE RULES! Or, If you mean, how to "get the gamecube files" running, then that's a different question. For your sake, I'll hope you meant the second one. I've never run any of the GC emulators, so I don't know this from personal experience. However, I would assume that you go to the "File" selection in the menu bar, and then select "open."
Hopefully that helps. If that didn't answer your question, then you'd better not ask it again, because you're not going to get an answer on how to download the games from here. Mouser X over and out.