Cats can purr from around one week of age. It is thought that it is a way of letting the queen (mother cat) know they have finished feeding. However, because they can purr with their mouth closed, they don't have to let go of the teat. It is a way of saying 'I'm content now'.
Cats have vocal cords and a larynx (voice box), just as we do. It is a part of the respiratory tract and the air passes through it on the way to and from the lungs. In fact your cat's larynx is made up of five pieces of