If you search this site, there should be a thread on this already. But basically it is a fat, round, plastic tube device that you blow into. It has a mechanism inside that vibrates, causing your chest wall to vibrate and loosen the mucus. You go through a series of blows then cough. Repeat 3 or so times until you feel the mucus has cleared. But like I said, do a search and you should come up with some more info.