Generating a sitemap by crawling your site
Enter your homepage URL and this tool crawls internal links starting from there - following only links on the same domain - and builds a standard XML sitemap from the pages it finds, up to 30 pages. For small sites and quick checks this gives you a ready-to-upload sitemap.xml; larger sites are better served by a dedicated crawler or a sitemap plugin built into your CMS.
Why a sitemap helps search engines
An XML sitemap is a direct list of the URLs on your site that you want indexed, submitted straight to search engines rather than relying entirely on them discovering pages by following links. It's especially useful for new sites with few external backlinks yet, or sites with pages that are hard to discover purely by crawling.
Why the crawl stops at 30 pages
Crawling happens live while you wait, within a short time budget, to keep the tool fast and responsive and avoid overloading either server involved. For a quick sitemap on a small site, or a fast check of your most important top-level pages, this is plenty - larger sites with hundreds or thousands of pages need a dedicated crawling tool or your CMS's built-in sitemap generator (most popular platforms have one).
What to do with the generated file
Upload the downloaded XML to your site's root directory so it's reachable at yoursite.com/sitemap.xml, then submit that exact URL in Google Search Console (and Bing Webmaster Tools, if you use it) so the search engine knows to check it directly rather than waiting to discover your pages organically.