There're many ways to create site map. Usually if your website based on Wordpress platform, you can use the plugin called Google Sitemap Generate or Yoast SEO
plugin to help creating sitemap.
Otherway, if your website is based on PHP or another platform, you need to create manually by using this webstie https://www.xml-sitemaps.com/
. Just enter your website on that website and create.
Hope this helps.