how to enable this script.

I downloaded the script where by pushing F6 you can take off the trees and rain and stuff, but how do I enable it. I downloaded it and it was in WinRar, and I opened it and I went to the application, but it just poped up as some stuff like F6 blah blah blah. So I put the file in my etmain, but then I tried it in et and it didn't work, what should I do?