The commands to manage assemblies are available from the Group menu Assembly submenu.
The Assemble command combines a selection set of objects, assemblies, and/or groups into a single assembly, and adds a Luminaire helper object as a head object.
The Open command lets you temporarily disassemble an assembly and access its head and member objects individually.
The Close command reassembles an opened assembly. For nested assemblies, closing the outermost assembly object closes all open inner assemblies.
Disassemble separates the current assembly into its component objects or assemblies.
The Explode command separates all objects in an assembly, regardless of the number of nested assemblies and/or groups, unlike Disassemble, which separates one level only.
The Detach command detaches the selected object from its assembly. If the object is a member of a nested assembly, after you detach it, it is no longer a member of any assembly.
The Attach command makes the selected object part of an existing assembly.