Inform 7 Home Page / Documentation
§2.11. Including extensions
We talk about "including" such an extension into a work of IF because the process merges rules and behaviours from the extension with those we have described ourselves. It's not uncommon for contributions by five or six different people to be pooled together this way.
Including an extension is only a matter of writing a single sentence in the source. For instance:
Include Locksmith by Emily Short.
Note that it is compulsory to name both extension and author.
Many extensions come with their own documentation. Again, follow the "Installed Extensions" link to see what's available from them.