There are times when you will need to group layers , and you don't necessarily have a parent layer in mind. This is particularly true when working with 3D layers, and you want them to follow an object.
Go to Layer>New >Null Object. Nulls are invisible but have all the transform properties of a regular layer.
Select all of the layers you want to parent by shift clicking to select a range or Cmd+click (Ctrl+click) to select noncontiguous layers.
In the parent column, choose Null1 or use the pickwhip.
Now you can set keyframes on one layer to control a group of layers. This is especially great when you want several layers to rotate around a point in space.