Site Maps - HTML and XML
Site Maps help human visitors and Search Engine Robots find content on your website. An HTML (ordinary web page) Site Map can provide a comprehensive listing of all pages on a site. With large site, navigation on a particular page will generally not include a link to every other page in the site. A Site Map can help people find content that they don't see on menus, drop-downs, etc.
As an example, visit the Sastrugi Marketing Site Map
XML Site Maps help bots find all the pages in your site. If your site has a tall pyramidal linking structure, and/or pages that are many links away from the home page, these pages may not be crawled by search engines.
You can create an XML Site Map, and learn more about XML Site Maps here