The steering system allows the driver to change the angle of the front wheels (and in some cases, the rear as well) so the vehicle can change direction. The component the driver uses to do this is the steering wheel.
Starting at the steering wheel the driver holds on to, a common design leads the driver's movements down a shaft (which often has joints in it so it can fit through points in the frame and around other parts) into the rack and pinion (which hydraulically assists the driver via a power steering pump) which has inner tie rod ends at each end. These are connected to outer tie rod ends, which are bolted at the ball joint to a steering knuckle. The knuckle is part of a larger assumbly which holds the wheel hub, and pivots on a ball joint on the lower control arm. At the top, it is either connected to an upper control arm (with another ball joint) or a strut. The hub contains a number of wheel studs (usually four or five, six on some heavier duty trucks, and even more on larger vehicles) which the rim of the wheel is mounted to, held on by lug nuts.
Electronic ("Drive by Wire") Steering
Some new vehicles are being produced with a steering wheel that just has a directional sensor and a feedback motor connected to it. The rest of the steering system is controlled by electric motors which operate based on the input from the steering wheel sensor.