To avoid confusion, let me distinquish the two types of sitemaps. One is the sitemap page that user may find on a website that consists of a categorization of the various pages of the site. This is to help users find information.
Another type of sitemap is more technical and is actually and XML Sitemap, or sometimes people refer to it as "Google Sitemap". This sitemap, user do not generally see. But it is usually auto-generated and then submitted to search engines.
We are talking about this second sitemap here. For example, here is the XML sitemap for LearnWebDesignOnline.com.
As part of Search Engine Optimization it is often beneficial to generate and submit a sitemap to Google and other search engines. Before generating the sitemap with the URLs of all your pages, consider converting your web application to use Search-Engine Friendly urls if it is not already.
Many open source applications has sitemap modules or plug-ins that you can install to generate sitemaps. Here are some examples ...
After you have generated your sitemap, it is time to submit it to search engines. You can submit sitemap via http request as described by sitemaps.org. You will need to url-encode your sitemap url and also you will need to know the search engine submission url. The sitemap submission URL for the major search engines are listed in Wikipedia. And you can use Albion Research URL encode tool.
Here is more info about how to submit by Google and Ask. You can submit to Yahoo at Yahoo Site Explorer under "Submit Site Feed".
If you sign up into Google's Webmaster Tools, you can setup a "site" and submit your sitemap to Google via the tool. Learn more by watching Google's video of their tools.
You can also let search engines know about your sitemap by specifying it in the robots.txt file. That way when the search engine crawler finds your robots.txt file, it will also see where your sitemap is located.
Here is some tutorials on how to specify your sitemap in the robots.txt file.
