Does anyone know how to make a pop up ad in HTML?

[Courage the Cowardly Dog]

I'm working on a website and i'd like to have a pop up gif ad that can be clicked to go elsewhere.

We never went over this in my web development classes in college. Either that or I was watching flash cartoons at the time.

here is the image in question.

http://content.ytmnd.com/content/4/0...7bce8747e4.gif