If you look at the top header for this page you'll see that it's called intro.asp. Despite that, if you hit view source on this page, it will appear to be a standard html page.

This is because ASP create HTML pages dynamically ("on the fly"). The way they do it is typically pretty straightforward, as you'll see:
On a page like this one, the HTML is typically written first, with only a few lines of ASP that make it dynamic.