The exhaust system is complex, with exhaust manifolds, catalytic converters, mufflers and pipes. The internal combustion engine is a giant breathing machine. Air and fuel go in one end, are ignited to generate the power stroke, which powers the car, and the burned exhaust gases are pumped out and carried away via the exhaust system.
The exhaust manifold removes the hot exhaust gases from the combustion chamber. It is typically cast out of iron to withstand blistering exhaust gas temperatures. The manifolds are tuned.to provide a smooth free-flowing, yet slightly restricted, passage for the gas to escape, which creates a "venturi" effect to speed the air flow away from the engine. This works in a manner to constricting the end of garden hose to create a stream of water that goes further in your yard.
Mufflers and resonators are designed to quiet the sound of the engine's exhaust, which can be quite abrasive if allowed to be uncapped (think: motorcycle). The mufflers and resonators have baffles or passageways built into them to route exhaust gases in a manner to produce a sound muffling effect.
Catalytic converters are designed to lower exhaust emissions, by creating a chemical reaction using a chemical catalyst (hence the name catalytic converter). The converter's catalyst heats up to cherry-red when hot exhaust gas flows through the converter, which creates a secondary burning of any residual hydrocarbons in the exhaust flow. When the engine's performance system is malfunctioning, more unburned gases are passed through the catalytic converter than it is able to burn, and the gases fuse with the catalyst forming a blockage. Exhaust flow is reduced drastically and the car loses power, sometimes even emitting the pungent odor of rotten eggs.
When the exhaust system has problems, airflow is affected and the engine control computer tries to compensate for the malady. Transmission shifting, electronic engine controls, fuel delivery, and emission systems are impacted. There us a possibility of fire from overheated exhaust components, and you can burn out the engine's exhaust valves due to excessive exhaust back-pressure.