I am asked many times a week if a site needs an XML sitemap and what the purpose of a XML sitemap is for.
Sitemaps are used to help the search engine spiders such as Googlebot, Bingbot, and other bots know about your sites at a much faster rate and index those pages in a manner that will help the webmaster / site-owner.
Think of streaking down the street and everyone can see your business, a sitemap is streaking for spiders. The spiders can see your whole site without having to guess on the pages and dig through your website.
There are a few things to remember, you can only have 50,000 URL’s per sitemap. Now that is not to say you can have 50,000 links to 50,000 sitemaps that each have 50,000 links in them. I would be impressed if you do and then ask why as that would be about 2.5 billion pages. I have not come across a site with rich unique content on it that has 2.5 billion pages. If you do, let me know, otherwise it is spam in my book.
After you pick a way to build your sitemap (there are many ways to build a sitemap for free, Google it) then implement it on the root folder of your site. The sitemap should be a XML file and should be found at:
There are other versions if you have many pages on your site like a .gz sitemap. If you do have the need for that I suggest you research the proper way to accomplish that task. I am also betting that you have developers to help your site as well.
I would also include the file in your robots.txt file like I did with this site. If you visit the below link you will see what I am disallowing and letting the search engines know about the sitemap.
If you have any questions please go find me on Google+.