As with all other modules, each profile can have its own set of documentation or you can have one set for the entire site.
Rather than building some fake documentation just for the demo system, you can see how the real documentation module works on for the entire system here:
Jamroom CMS Docs: "Table Of Contents"https://www.jamroom.net/the-jamroom-network/documentation/contents
Jamroom.net is built with exactly the same CMS as you download so anything you see on jamroom.net you can build in your site too.
There are many types of sections you can add to a document
Once the section is complete, you can rearrange and edit them to complete your docs.