You turn a knob and the sun roof opens. Another switch pops the trunk open. You open the glove box and discover it is empty. Sometimes, when you buy a used car, you get all kinds of freebies. When you start searching around, you might find the owner's manual, maintenance manuals, old repair records and other things belonging to the person who last owned the car.
Money is always fun to find.
Sometimes, when you buy a used car, you get nothing. For some reason, all manuals of any kind were removed from the car and the only way to find out what all the switches, knobs and buttons do is to just start trying them. Owner's manuals are kind of important. Without an owner's manual, you won't know the recommended oil for your engine, gas tank capacity or how to set the correct time on your radio. Repair manuals such as Haynes and Chilton often cover many different models of cars.