Sitemaps are files that list each post and page that should be indexed by search engines like Google or Bing. Jetpack allows you to generate such files thanks to the Sitemaps feature.
To add a sitemap to your glow blog you just need to Activate Jetpack and then the Sitemaps module in the Jetpack section of your blog.
After that you can see your sitemap at: yourblogurl/sitemap.xml
for example this blogs is at https://blogs.glowscotland.org.uk/glowblogs/jetpack/sitemap.xml
These pages are for search engine, not human beings but you can embed a sitemap using the [sitemap] short code:
As this blog is mostly posts it does not have a very interesting sitemap.