To create a group

To create a group of model objects, use the following procedure.

If you have previously selected one or more model objects, you can add those to the group automatically.

Either:

on the Catalog ribbon tab, select the Group tool in the Groups group

or
right-click in the View window and select Groups > New Group from the pop-up menu

The Group Manager dialog opens.
Type the Name of the group.
(Optional) If you used the right-click pop-up menu, then the selection set will be added to this group automatically. You can filter the objects added by clearing the Include check boxes.
Click OK.

You can now add or remove model objects in the group.