Assembly->Create creates a new assembly.
Assembly
The 
Assembly entry provides a name for the assembly object. 
This is optional: when empty (or filled with separator characters, 
as space, tab, newline), the assembly will be named Assembly.
Object identification is explained in 
Introduction Identification.
An assembly is a container whose primary purpose is to contain other objects.
When an assembly is created, it has no child objects and consequently no visual
representation. The only way to select an empty assembly is therefore to write
its identification or to use the mechanisms provided by 
Assembly Select.
To avoid this problem, when 
Ok is pressed and the new assembly 
is created, the 
Assembly Create dialog is automatically replaced 
by the 
Assembly Link dialog, with the new assembly identification 
already inscribed on it. How to link objects to a assembly (TODO) is 
described in the section 
Assembly Link.