The above contains all you need to get started. The story file provides an example of how to get started (along with the few required commands) and the extension is (lightly) commented. If you would like help getting started, start a thread in the forum or if you have more general questions, I suggest checking out the incredibly helpful examples in the Inform source code.
The above is written in Inform 7. You need to download Inform 7 to get started.