CAN ANYONE EXPLAIN IT?

A sitemap is a blueprint of your website that help search engines find, crawl and index all of your website's content. Sitemaps also tell search engines which pages on your site are most important.

If you use WordPress, you can get a sitemap made for you with the Yoast SEO plugin.

What if you don't use WordPress?

No worries. You can use a third-party sitemap generator tool like XML-Sitemaps.com. These will spit out an XML file that you can use as your sitemap.