Basically, a site map is a layout of a website’s content. It is designed to help both search engines and users navigate the site. Site maps are like the layout maps in large shopping malls, which helps you find different departments. A site map can be an organization chart, a hierarchical list of web-pages (with links) organized by topic, or an XML document that provides instructions to search engine bots.
A sitemap tells the search engine crawler which files you think are important in your site, and provides vital information about these files: e.g., for pages, how often the page is changed, any alternate language versions of a page and when the page was last updated etc.
Below is an Example of Sitemap: