To use it, you'll need to have the website saved in some folder on your system where Free Offline Site Map generator can access it to analyze it and establish its structure.
Free Offline Site Map Generator works in two formats: XML and HTML. The first of these is the protocol used by Google Sitemap, and using it will help your site get a better ranking on Google. The other format is recognized by all the other popular search engines, including Google.
And you can always choose to generate maps in both formats, including them in the root folder where your website is found to assure that it is well-placed on any search engine.