Sitemaps are VITAL to any website. They tell google whats going on with your website, whats new, and allow the spiders to quickly crawl your website and move on. Without a sitemap there can be many pages left out because google cant easily crawl them.
Two types of sitemaps:
- HTML
- XML
HTML sitemap:
This sitemap is intended for users. Its manually updated with the important links you want people to access quickly. These are also not very common anymore.
Example: https://www.xml-sitemaps.com/sitemap.html
XML Sitemap:
This one is auto built by wordpress. Its a live sitemap that is updated instantly when a user or client adds a blog post, page, etc.
Example: http://protkdmac.com/sitemap_index.xml
As you can see there sitemaps within sitemaps. It also shows last modified date and time. This is for google