I do not fly the aircraft in question, so feel free to correct me if I'm wrong.
I would liken manual reversion, to driving your car, without the power steering working. In normal operation, cables link the control column, and rudder pedals to various hydraulic power control units, which actuate the control surfaces.
If both hydraulic systems were to fail, then it is possible to move the control surfaces by a direct link between the cables and the flight controls. To assist in the huge control forces that are required to move the various surfaces, tabs and aerodynamic balance panels are used to create a pressure differential, and therefore lighten the physical effort required to control the aircraft.