Hey I am the author of fedipage, sorry im just seeing this. I am happy to help.
So for starters the documentation is pretty much the readme. It goes over, step-by-step, how to setup an instance.
As for the point, its largely so you can host a static page, like a blog, and have that page look like and be interact-able as if it were a fediverse/mastodon instance. In other words you can follow the instance as you would someone from the fediverse. New posts (pages, blog posts, whatever) will show as a post ont he fediverse and show in followers feeds. Their comments and replies to post will show as comments on your blog attached to the particular blog post, etc. Boosts and likes also will show up on yoru blog page.
It basically lets you have a static site generated that has all the features of a fediverse account more or less.
Hope that helps, let me know if you have any questions. For reference the fedipage git has the instructions int he readme here:
https://git.qoto.org/fedipage/fedipage