What's that thing called when young boy racers put on there car to make it sound loud?

Is it the exaughst? And where can I put this on my car (ford focus 04 three door 1.6) I want that cool loud sound on mine, so where do they get this these young kids? And how do I go to a garage and explain this to them? And will I look stupid asking the question to the garage worker?

It is the exhaust… But beware! The cops will notice you more. And if you don't tell your insurance you have modified the car. And you have a problem. Does not have to be yor fault. Then you will find yourself with no insurance! And they tell the national register… Then you will be back on that red 57 seater