After Effects Technique: How to use the Luma Matte attached at the end of the stock footage?

So you’ve just purchased an awesome stock video or stock animation and you want to lay it on top of your footage in your edit. But how do you go about doing that, and what is that black and white segment at the end of the clip?

This black and white segment is called the Luma Matte – and is to be used for making parts of the footage transparent. This tutorial teaches you how to use the matte effectively in Adobe After Effects.