There are a few different steering systems used in modern automobiles, and most cars use a rack-and-pinion steering system to control the car. Since the wheels are supporting the massive weight of the car and its passengers, the system is designed to make it easier to turn the wheels. Often, it is supported by a power steering system so you are not getting a workout every time you need to turn a corner, and in this case, the setup is slightly different than a traditional rack-and-pinion setup.
The steering wheel attaches to the steering rack by the steering shaft. When you turn the wheel, the rack translates these movements into linear motion to turn the wheels the way you want them to go. There is a cylinder in the rack that contains a piston, with a fluid port on either side. High-pressure steering fluid, when applied to one side of the piston, forces it to move. This movement affects the rack as well and facilitates its movement, so you do not need to strain when you change the car's direction.
At the base of the steering shaft is a small device called a pinion. This little gear spins when you turn the steering wheel, which is how the rack moves back and forth to change the wheels' direction.
Now, when it comes to turning, the inner and outer wheels need to be able to move relatively independently. Consider a record spinning on a turntable, and imagine two objects resting on its inner and outer edges. The item on the inside does not travel as far as that on the outside, but they still make one revolution in the same amount of time. When you turn a corner in a vehicle, the same basic principle is at work. The outer wheel must travel farther than the inner wheel to complete the turn, and in order to do this, it has to be at a different angle.
This is where the tie rod comes in. Tie rods transmit the force of the moving rack to steering arms, which are welded onto the wheels to make them move in the necessary direction.
If any of the components in the steering system break down or malfunction, the risk of accidents is greatly increased, as you can have difficulty steering or even lose control of the car.