How do you do that "e-mail this movie to a friend"

I’m brand new so take it easy on me. I have noticed that at the end of some movies is a button that says e-mail this movie to a friend. How do you add that to a movie. Also when the friend gets the movie is it an attachment or is it being played from my web server or what?

Basically I want to let people forward the movie to all the friends they want while conserving bandwidth.