mask in animate 3?

I see in the manual that you can have a mask on a layer or more but it´s difficult to understand how you add this mask and how it works.
Anyone know how to understand it?

/ Mattias

Here is a link to tonyteach about masking in ToonBoom Animate vs Flash. I think you’ll get what you need there.
http://youtu.be/rMerzR7XSy8

Good tutorial.