Convert a layer into a track matte

Using a track matte is similar to using the Preserve Underlying Transparency option, which causes a layer to get its transparency from the transparency of the composite of the layers below it in the layer stacking order. 

Five types of track matte：

The following is an example of no Track Matte

The following is an example of Alpha Matte

The following is an example of Alpha Inverted Matte