Assigning a Unit Object to a Parent Object 
Packages, worksets, roles, and pages are portal objects that can contain other object types. For example, roles typically contain worksets, and pages contain iViews.
An object that contains other objects is called a parent object. The objects nested within a parent object, are called child objects.
Before a child object is assigned to a parent object it is first created as a unit object (also referred to as a standalone object or building block) in the Portal Catalog.
To assign a unit object to a parent object, such as a workset, role, or page, you first open the parent object in its respective editor, and then you select the unit object from the Portal Catalog. Note the following:
Child objects are delta link instances of the unit object from which they are derived.
While unit objects are displayed in the Portal Catalog, child objects embedded in a parent object are not. To view the child objects assigned to a parent object, open the parent object in its respective editor.
To determine the source objects of an embedded child object or unit object, use the delta link tracer. See Tracing Delta Link Dependencies.
For more information about object instance types and how they relate to one another, see Content Object Model.
Procedure
Launch the Portal Content Studio. In the top-level navigation bar, choose
Content Administration 
Portal Content 
.Open the parent object in its primary editor. See Editing an Object.
In the Portal Catalog, right-click the unit object that you want to add, and then choose the relevant option to add the content:
Page Editor: add iViews and pages to create a page. See Adding Content to a Page.
Workset Editor: add iViews and pages to create a workset. See Adding Content Objects to Roles and Worksets.
Role Editor: add iViews, pages, and worksets to create a role. See Adding Content Objects to Roles and Worksets.
Package Export Editor: add iViews, pages, roles, worksets, systems, and layouts to create a transport package. See Filling an Export Package with Contents.
Result
A delta link instance of the unit object you selected in the Portal Catalog is added as a child object to the object that is currently being edited in the Object Editor.