Putting animatoin to a movie clip

how do you put your animation to a video clip?
like in the movies!

Like this: http://blenderartists.org/forum/forumdisplay.php?f=14

using the blender compositor.

were can I download it?

It’s already built in Blender.
You just have to learn how to use it.
I suggest checking out the blender guru tutorials, he teaches a lot about render nodes.