Over there is where that human in the seat wants to go. I need to roll into a 22-degree bank to get there. Better haul away on the aileron cable. So the computer commands a servo to move, yanking the controls to do its bidding. Those are the controlling bits, things like servo motors, clutches, capstans, cables and chains.
Flight control is a loop or series of loops.
As the autopilot computer yanks the chains, it expects to see things happen. Some feedback is often sent from the servo, in the form of a position sensor or motor feedback. Plus, if all is going right, the airplane will go in the direction the computer's electronic brain wants it to go. It's the loop-iness of autopilots that gets the technician and pilot into trouble. On the ground, you have no loop.