A sitemap is a file that includes information about the pages and files on your site, which search engines like Google use when crawling your site.
A sitemap is automatically created for your Thinkific site and you can access it at: https://yoursite.thinkific.com/sitemap.xml
Simply replace yoursite.thinkific.com in the above URL with your Thinkific URL and you'll be able to access your sitemap!
You can read more about what sitemaps are used for here: Learn about sitemaps
Can I customize my sitemap?
You can’t customize the xml file directly, but it does automatically pull changes made in your SEO fields. Check out how to customize your SEO here: SEO - Search Engine Optimization