What is an assembly ?
In a modeler, an "assembly" represents a grouping of interrelated parts, that remains or not relative movements between these pieces.
A component of an assembly can be :
It is possible to create a part directly in the assembly, so as to build it in its correct relative position. In this case, there may or may not be links between parts.
Construct by kinematic equivalence classes
A kinematic equivalence class is a set of parts integral with each other, or animated with the same movement with respect to a given referential (same nature of movement, same direction or axis, same speed, same acceleration, ...).
1- Construct each kinematic equivalence class
Each kinematic equivalence class is itself an assembly (which can sometimes be reduced to a single part).
Primordial step, the choice of the reference element :
The reference element of your assembly (or under assembly) will be immobilized; it is therefore the other elements of the assembly that will be put in place with respect to this one (whether they remain mobile or not).
2- Build the main assembly
The same procedure as above applies for the construction of the main assembly.