Refer to figure.
In a hydraulically powered flight control system the pilot operates the controls, these can be a sidestick and rudder pedals or a conventional yoke with rudder pedals. These controls are fitted with transducers which convert the mechanical movement into an electrical output which is then amplified and processed by several computers. These computers provide the input for the servo valves which controls the movement of the hydraulic actuators attached to the flight control surfaces.

In conclusion, the actuators convert the hydraulic pressure generated by the pumps into control surface movements.