For a website sitemap is very very important. Normally there are two types of sitemap one is xml sitemap and other is html sitemap .XML sitemap for the web crawlers and HTML sitemap for the website visitors.
XML sitemap is an xml file contains list of URLs of a site. It gives search engines useful information about your site such as list of URLs on your site, How often the pages on your website change, last modified date of each page. Html sitemap helps the visitors for easier navigation. It is easy to create sitemap using tools than manually.