Generally there are two types of sitemap, HTML sitemap and XML sitemap. HTML sitemap stands for Hyper Text Markup Language sitemap and XML sitemap EXtensibleMakeup Language sitemap.
A HTML sitemap is used to list all hyperlinks or the link of all pages of website into a single page.These hyperlinks are normally listed hierarchically and they may provide a description for each link. Adding a HTML sitemap to your website will help your visitors navigate and find information easily. So a HTML sitemap is mainly created for humans. Although a HTML sitemap is created for your visitors, indexing bots such as Googlebot might have a better chance to crawl your first-time-missed links again since all the files are well put together in your sitemap page.
An XML sitemap is mainly for search engine crawlers not for visitors to a website. It allows webmasters to inform search engines about URLs in your website for easy indexing. Submitting a XML sitemap to search engines such as Google, Yahoo, and MSN will not only help your website being indexing rapidly and proficiently but also increase your website’s visibility in search engines as well