Exhausts have four main functions: to control noise, to direct exhaust fumes away from passengers, to improve the performance of the engine and to improve fuel consumption.
An exhaust is a series of pipes that links the engine to a silencer and a catalytic converter.
The tailpipe is the part of the exhaust that you can see extending from the back of the car. The silencer joins onto the tailpipe, then a series of further pipes joins the silencer to the catalytic converter and then the engine.
The silencer contains metal plates or tubes that have a series of holes bored into them. Exhaust gases leave the engine at very high pressures, and the holes in the silencer help to reduce that pressure so that they leave the car more quietly.
Exhausts can corrode from both the inside and outside. How long your ehxaust lasts depends on how far and how often you drive your car rather than the length of time it has been fitted. Vehicles used for short trips around town tend to corrode their exhausts in a much shorter time and distance than cars used predominately for long journeys.