Load Movie from Library into Container Clip on click

I’m getting back to scripting after a loooong time, and i’m feeling quite rusty. I need a little help with this:

I have a contaner clip on stage, along with four buttons. Upon clicking each button, the script should load a movie clip from the library into the container clip on stage, after unloading whatever was previously contanied in the clip.

How do i point the button to the movieclips in the library?