To begin, in the present build you need:
- Hades Core
- Crystalite Production Unit (CPU)
- Basic Assembly

The Crystalite Production Unit, converts Stone (formerly iron ingots) into Crystalite ore.
This Ore goes into the Hades Core.
The Basic Assembly makes it into plates.

CPU --> Hades Core --> Basic Assembly.

Assemblers, form the basis of the Tech Tree, using parts made from the previous tier with newer parts used for the next.
So you can't build Tier 3, without Tier 2.
The requirements of the Parts also increase, in

Basic Assembly
--> Prototype Assembly (EC or PC)
--> Tier 1 Assembler (EC or PC)
--> Tier 2 Assembler (EC or PC)
--> Tier 3 Assembler (EC or PC)
---> Tier 4 Assembler (EC or PC)
---> Tier 5 Assembler (EC or PC)

Weapons-tech generally, begins on Tier 2.
Reactors flow between 2 & 3 for starting positions.