There are two types of sitemap. One is sitemap.xml and other is html sitemap. Can you specify that which sitemap you are willing to know.
hi site map used in the site portals to make navigation easy, it contains the links of the pages which are in the website.
Sitemap provides a gist of all the links of a website facilitating both search engine crawler and users. It as well serves as a navigation for users.
Sitemap has two forms. One (xml sitemap) is for the crawlers so that when they crawl your site, they has have something to follow depending on the priority level set on each page. The other sitemap serves as a table of contents for users online that are searching for pages on a website that they cannot find.