To manage layers in CAT, use the Layer Manager rollout.
Layering Concepts in CAT
The Layer Manager (CAT) rollout is available for every bone in a CATRig. To access it, select any bone in the rig and go to the 
Motion panel.
Layers are Applied to an Entire CATRig
With CAT's layering system, whenever you add a new layer, that new layer applies to every bone in the CATRig. There’s no such thing as an arm layer or hand layer. When you add a new layer, every bone gets that new layer, and you can choose the parts of the CATRig that should not use the new layer. This process is called Feathered Weighting.
All Basic Layers Contain Standard Max Controllers
The layer system in CAT is simply a mechanism for holding and managing animation controllers. It supports all 3ds Max animation controllers, including all the various keyframe controllers such as Bezier, TCB, Linear, Quaternion, and Euler, as well as the procedural controllers such as script and expression controllers and constraints.