not sure if you watched the video on their site, because that seems pretty self-explanatory (especially from 1:18 onwards) It also says clearly on the site that it is a one page and very basic theme:
a page for documentation with a simple way to navigate between sections, and a basic page template for simple pages like a Changelog
So if you are looking for how to add Posts that are not “Sections”, then you have perhaps downloaded the wrong theme?