A typical XML Sitemap file lists each URL, together with information about when it was last updated, how often it normally changes, and how important it is, relative to other pages in the site). This helps search engines to more intelligently crawl your site.
Some hosting providers (for example 1and1) provide utilities via their web control panel, to create your sitemap, so you should always check with your provider first. If this service is not available, then make a visit to xml-sitemaps.com and enter your site URL into the generator box. Copy-and-paste the resulting sitemap into notepad, then save-and-upload to your site with the file name: sitemap.xml. The process is done through their user interface and will also allow you to check on the number of indexed items. To submit your sitemap to Google, you must first add your site to Google Webmaster Tools. Then, as described by their help page