Sitemap is a hierarchical representation of all the links that are present on your website. It comes with two extensions. One is with ".html" and one is ".xml". Both have their own purpose. The ".html" extension is for humans to easily be able to navigate through your website. The ".xml" representation is for the google web crawlers to be able to read the website links and index them.
Yoast SEO plugin is provided by the Yoast team which has been in this game for long. Yoast SEO plugin helps you to manage your SEO easily. This is one of the most popular plugins along with RankMath.