You need to setup a web server software first, like Web server - RaidenHTTPD official homepage, An easy to use Web Server software for Windows, Apache, IIS replacements (RaidenHTTPD web server)

then name your web page as index.html or index.htm under the web root directory so people can see it as default page of your web site.

extension name is just used to tell the windows or browser about its file type and association to opener programs like IE.