An XML sitemap helps search engines index pages on a website by providing metadata like page priority and change frequency. The document outlines a 5-step process to create an XML sitemap: 1) use an online sitemap generator, 2) download the sitemap file, 3) edit priority and frequency using Notepad++, 4) finalize the sitemap, and 5) submit it to Google Search Console. Maintaining sitemaps is important for search engines to understand a website structure and for pages to be properly crawled and indexed.