Re: throw our pto bearing?
I don't want to sound condescending, but every manual transmission has a throw-out bearing- it's one of the most critical pieces to clutch operation.
As far as PTO's (PTO- power take off) go, they are a handy accessory that can be attached on to many manual transmissions, that are essentially another set of gears that can power a variety of things- winches, pumps, farm implements, your friends generator, etc.- and are very handy, indeed.
Most all good sized tractors have them, and on tractors especially, they can be very dangerous. People get chewed up by them every year. Anyhow, this isn't a detailed explanation, but I hope it helps.