How the sitemap are works?

Sitemaps:

The "Site-map" are two types:  HTML Site-Map and XML Site-Map.
     Site-map is a  way who tells the search-engine (Google, Yahoo, MSN etc.) about the web pages of your web-site we may not or else notice. When we submit our  site-map in the server then the Google knows the all about of our XML pages on our web-site, including page-URLs that might not be find by the Google's usual crawling process. 
     In some websites we see that the 'site-map' are shows in the head part of the page is also known as the HTML site-map, by using this we can jump any other link-page of the web-page.
      Site-maps are mostly helpful if your web-site have dynamic contents or your web-site have bulky store of content pages that aren't correctly linked to each other.
   It's not sure that the Google crawl or index all of our web-site URLs. Google also provide the site-map tool for creating the site-map of any web-site.