the throwout bearing is what the clutch fork uses to push on the fingers on the pressure plate, basically it allows the stationary fork to contact the spinning fingers without things rubbing together. It is a sealed bearing, meaning that the only lubrication it gets is whatever was sealed inside the bearing when it was new, which is why you shouldn't sit at lights with the clutch in. The bearing is not designed to spin for long periods of time. I would get it replaced soon. You will have to drop the
tranny to replace it, but its not too hard.