Sitemap is basically an xml file which tells search engine the page structure. This makes it easier for crawling for search engines. it is not mandatory to add sitemap. My website saupra.com is popular but I havent made a sitemap .
Sitemaps are an easy way for webmasters to inform search engines about their website pages on their websites,which are available for crawling.It is an XML file that lists URLs for a site along with additional metadata about each URL,so that search engines can more intelligently crawl the site.
A sitemap is a page in your website where you can find the list of pages/posts of the website. Sitemap makes it easier for the crawlers and users to navigate your website.