A sitemap is a list of a website's content (pages, links, media, etc.) that Google uses to index a website in search results. Sitemaps are useful for websites with hundreds of pages.
B12 websites are built to not need sitemaps, and therefore we don't offer them. Google regularly crawls the web to add new websites to its search results, but if you're concerned your website is not in search results, you can request indexing by adding your website to the Google Search Console.
If you have any questions, email us at firstname.lastname@example.org. 😃