The intent of a sitemap is to provide an index of the website contents. There are two types of sitemaps - one for website users and another one for search engines.
Sitemap for Website Users
This sitemap should be a regular web page (htm, html, etc) and display an index for the website pages. Sometimes a website viewer will not find what is being looked for and will go to the sitemap page to find links for everything in the website. Include a "Sitemap" link near the top of the home page and it can also be included at the bottom of each page. Click on the links below for examples of sitemaps.
Sitemap for Search Engines
This sitemap is a special non-web page format file that must be uploaded to the main (top level) folder for your website on the host server. It should include the URL for each website page that you want search engines to know about. This type of sitemap is not required but it insures that search engines will find all of your web pages. The sitemap must be in an acceptable format or the search engines will not use it. There are several formats that can be used - TXT and XML are the most common. If you are not familiar with XML coding a simple text file works fine but it must be created with a text editor (like Notepad) in UTF-8 format. DO NOT use a word processor like MS Word as they include formatting code that will make the site map unusable. Following is an example of a TXT sitemap.
Google Webmaster Tools
Google is the number one search engine and they have very good webmaster tools that allow you to submit your site map so they will know about it. They also have options that let you see if your website is in their website database and if the Google robot found any errors in your website (unreachable pages, etc). You can also view Google statistics for your website.
Sitemap Design Information