The throwout bearing (TOB), also known as the release bearing, is the contact between your left foot and the rotating clutch disk that allows it to be moved away from the engine's flywheel. When the TOB wears, you hear the whirring noises as the spinning clutch disk grinds on the damaged bearing when you press the clutch pedal. This will continue in degrees of greater damage until the thinner TOB (probably now without its ball bearings - like mine) will not provide enough travel for even a fully depressed clutch pedal to cause the clutch disk to disengage the flywheel.
The only solution is to remove the clutch and transaxle (not a simple process) and replace the throwout bearing. After exerting the great amount of effort to access the throwout bearing in the clutch housing, it would be foolish not to replace the other wear items that are accessible during the service. These include the clutch disk and pressure plate, the rear main crankshaft oil seal, the axle seals in the transaxle and synchronizer blocking rings if any grinding has been heard during shifts.
You can shop around for individual parts, but SHO NUT Performance has conveniently and economically packaged many of the normal wear items into several clutch and transaxle packages. I myself have a SHO parked in the garage that is awaiting delivery of one of Josh's clutch kits and a few other transaxle parts. He has a video and written procedure to bring this job almost within the realm of the average shadetree mechanic.
If your clutch is making whirring or grinding noises when you depress the clutch pedal and the clutch disk will not fully disengage the flywheel to allow shifting, you certainly need a new throwout bearing. You will be very well served by also planning to replace the clutch disk, pressure plate and rear main seal. If you have any leakage from the transaxle shaft seals, this is also the time to replace them. No fooling.