When you save an HTML file, you can use either the .htm or the .html extension. We have used .htm in our examples. It might be a bad habit inherited from the past when some of the commonly used software only allowed three letter extensions.
With newer software we think it will be perfectly safe to use .html.
And I think you need to improve yourself, fast. Else your friends will not be friends any more. Besides, it's not even stinkey winkey n00b. Ask Uncle Hendrax about that.