Protoforms are the starting point for Cybertronians. They are built in a variety of types and models.
Once a Spark is created by Vector Sigma and placed in the protoform's Spark Chamber the protoform is moved to the final assembly station.
The Spark is in a preconscious state and as it interacts with the data preprogramed into it's Memory Core it influences the protoform, and the protoform influences it.
In a sense Cybertronians create themselves.