Hey there! I'm a Python dev, so I might be able to help.
Never heard of Ren'py before, but it looks really awesome

(assuming this is it:
http://www.renpy.org/wiki/renpy/Home_Page)
AFAIK, there's 2 levels of programming: regular, story telling levels, and then the actual Python programming.
If you are doing Python, you need to import the library.
Then assign keys to certain functions and such

Of course, this is just speculation. I need to know what you are trying to do first, then
we can approach the problem.
