A car's steering system is composed of several components that work together to provide directional control of the vehicle. These components include:

1. Steering wheel: The steering wheel is the primary input device for the driver to control the direction of the car.

2. Steering column: The steering column connects the steering wheel to the steering gearbox or rack and pinion, allowing the driver's input to be translated to the wheels.

3. Steering gearbox or rack and pinion: The gearbox or rack and pinion translates the rotational input from the steering wheel and column into lateral motion that moves the wheels.

4. Tie rods: The tie rods connect the steering gearbox or rack and pinion to the steering knuckles on the front wheels, allowing the lateral motion to be transferred to the wheels.

5. Steering knuckles: The steering knuckles are the pivot points for the front wheels and allow them to turn left or right.

6. Power steering pump and hoses (if equipped): The power steering pump and hoses provide hydraulic assistance to the steering system, making it easier for the driver to turn the steering wheel.

7. Steering fluid reservoir (if equipped): The steering fluid reservoir stores hydraulic fluid for the power steering system.

These components need to be replaced for various reasons, such as wear and tear, damage from accidents, or malfunction due to age or misuse. Over time, parts such as tie rods and ball joints can wear out, causing play or looseness in the steering, which can be dangerous. The power steering pump and hoses can also fail, leading to difficulty turning the steering wheel, which can affect the driver's ability to control the car. Regular maintenance and inspection of the steering system can help identify potential problems before they become serious safety issues.