I downloaded it but I don't know how to use it
Oops. I had to right click and select "Open With Other Aplication..." then select "Autorun Prompt" and tick the box "Remember this application for "executable" files" then click "Open".
I'm not sure why it was trying to use some other application to open it. I probably just messed it up somehow. Anyway, thanks. It's a pretty interesting game.