Understanding XML Sitemaps

Search Engine (google, yahoo, bing,..) is a kind of application that build for checking online website in order to get (index) their content. However, this robot or software are different from human and it is possible that some of your post or page will not found.
You should find any way to optimize your website mean to make Search Engine easy to index your site.
XML Extensible Markup Language it is a standard of machine readable format consumable by data munching programs like feed readers especially search engines. it containing of information(url that make up) about website or blog. it is a small tool but useful SEO tool for webmasters interested to optimize web site.
In order to create XML file you may need tools xml sitemap validator plugin to create a file sitemap.xml and upload it in to your website ex. www.example.com/sitemap.xml and than log into web master tool like google and submit this url file.