The throttle cable links the car's accelerator pedal to the throttle. The accelerator pedal manages the throttle valve which controls the flow of air in the engine and in turn dictates the amount of fuel released into the engine.
The throttle cable is made from steel cable protected by a casing. When you press your foot down on the accelerator pedal it causes the throttle cable to move which opens the throttle valve, allowing more air to run into the engine of the car, ultimately causing acceleration.
Being the cable that joins the accelerator pedal to the throttle, the throttle cable is subject to a great deal of action, resulting in wear and tear and damage. The throttle cable can eventually erode from sustained use and will need to be changed with a good quality replacement.
If the throttle cable is run down, broken or faulty in some way, you won't be able to control your car's acceleration properly, so the accelerator throttle cable is crucial in ensuring the engine is getting the correct amount of air and fuel, allowing you to control the speed of your car.