In the Design Director, "Categories" refers to groups of objects - 2D, 3D, cameras, etc. You can insert a category into the Design Director in order to have easy access to zooming, visibility, and other properties of the object group.
Note: To add single objects to the Design Director, use Graphics.
To place a group of objects into the Design Director:
- Select the objects in the drawing space.
- In the Design Director select Categories in the upper pane and select Create New from the toolbar or local menu.
- Accept the default name or assign one that will help you recognize the object.
All object groups you add to the Design Director will appear in the lower pane. The lower pane contains the following options: 
ZoomTo: Zooms to the extents of the objects.
Visible: Displays or hides the objects.
Color: Sets the objects' pen color.
Add To Category: Adds the selected object to the category.
Remove From Category: Removes the selected object from the category.