Some graphics programs have what are called "Null" layers. These layers are invisible (do not render) but can be attached (or parented) to other elements in the composition to add movement to a group of items at once, and in relation to each other. Motion does not have null objects. Instead it uses layers and groups (if you are using Motion 2 then you have elements and layers, respectively...) If you want to animate a layer, you keyframe the layer. If a group only contains one layer, you can animate that layer by selecting the group or the layer. (The nice thing about that is that you can have a different anchor for the layer and the group, effectively giving you multiple joints to animate at once. Keep in mind that animating a group will affect all groups and layers inside that group.)

If you place several elements or layers into a group, when you animate the group, you will animate all of the layers in that group to the same degree.click here for movie For instance, if you place five squares in your composition and place them in a circular pattern, all contained in one group, when you rotate the group, all of the squares will rotate together, maintaining the original circular shape and orientation.