And I insert them by crafting them together or do I need a machine for that?
There are 4 grades of circuit board - supporting 1 thru 4 installed tubes.
The circuit boards are programmed by using the forestry Soldering Iron.
This gives a very confusing UI that makes it very easy to mess up the circuit board: The way to use it it:
* With the soldering active on your action bar, right click to open the UI.
* Toggle the mode between Manual Farm, Automatic Farm, Upgrade etc.
* Drag tubes from your inventory to the slots to set their function *1
* When, and only when, you are 100% happy with your selection, drag a circuit board - ensuring it supports as many tubes as you have inserted - into the appropriate slot. It will immediately consume the 0 - 4 tubes and appear, programmed, in the output slot.
1: Fill the slots from the top to the bottom if you don't intend on using the diamond (4 slot) circuit board. Also each of the the slots have a default function that requires no tube, and can be used in devices that support that function even if a smaller circuit board is used.
For example, A forestry multiblock farm always has 4 quadrants, so if you with to create a full sized Tree Farm (manual or automatic) you can used the cheapest quality circuit board as the default function for the slots that cannot be programmed is tree farm.
The other use of the Soldering Iron is to remove circuit boards from devices prior to moving them. Breaking a device with an integrated circuit will typically destroy the circuit, however if you open the device UI, and drop a soldering iron onto the circuit slot the circuit will be returned to you.