Containers can be used to store parts, assemblies, and associated tools such as workplanes, and workplane sets. Although the preferred owner of a container is a part, containers can also be owned by assemblies.
1. Click Structure and then, in the Part & Assembly group, click New Part, or New Assembly. The Create New Part or Create New Assy dialog box opens respectively.
2. To create a new container,
a. Click Structure and then, in the Part & Assembly group, click More.
b. Click New Container in the Tools section. The Create New Cont dialog box opens.
3. In any of the open dialog box, type a new Name.
4. Optional: Click Model Name and type a name. Model Name is the contents file name for the element when you save
3D Data files.
5. Optional: Type the name of a parent assembly in Owner if you want this element created as part of an existing assembly.
New Part, 
or New Assembly. The Create New Part or Create New Assy dialog box opens respectively.
to complete the operation.