We're in the process of rewriting Ren'Py's documentation. While what we have here is the most up-to-date documentation, it's also very incomplete. To find out more about Ren'Py, please visit the Ren'Py home page:
http://www.renpy.org/
Much of Ren'Py is only documented in the older documentation, which is stored in the Ren'Py Wiki:
http://www.renpy.org/wiki/