With hydraulic steering the helm is a pump. Turning the wheel pushes oil through hoses to a ram, or cylinder, which moves the outboard or the rudder. It's light to turn and takes no effort to hold against the engine's torque, and an autopilot can be added with its own pump in the same lines.

In this video I install a HyDrive hydraulic steering system in a boat: installing the helm and the ram, connecting the hydraulic hoses and bleeding the system.