Power steering uses a hydraulic pump to operate the steering rack located underneath the chassis of the vehicle. The pump cycles hydraulic fluid through a series of hoses that interlock throughout the steering system.
There is a reservoir located somewhere in the engine compartment that holds the power steering fluid. The pump circulates the fluid from the reservoir to the steering rack. From the steering rack the fluid makes its way to the pump to return into the reservoir.
The steering rack uses a set of gears the turn the wheels left or right. The hydraulic fluid fills the rack and pushes against a piston. When the wheels turn the fluid flows to one side and pushes the piston.