how exactly XML sitemaps work, as opposed to other types of sitemaps
an XML sitemap is intended to be read by a machine. it's a bland uninteresting list of what URLs exist on a site so that search engine spiders & robots can index your content.
the other kind of site map is the sort that a human uses to navigate your site. It's usually rendered in HTML (not XML), contains links that can be clicked on, is organized intuitively, and might show the organization of the site as sections, categories, or some other hierarchical tidiness.