Your manual transmission would not function properly without a working and intact clutch release bearing. If you "ride the clutch" rather than downshifting or dropping into neutral, then it will be engaged way too often. This over exerts the components of the clutch, and causes premature wear and failure. A common symptom of a busted or broken throw-out bearing is a loud squealing when the clutch pedal is depressed. This comes from miles and miles of unnecessary use, when all it was intended for was a momentary engagement and disengagement of the clutch disc and pressure plate. When it is broken, it will also adversely affect the diaphragm springs in the pressure plate causing that terrible sound you are likely hearing. Shifts will also become difficult and eventually impossible for the driver; ultimately rendering the car useless until it is fixed. Most clutch service includes replacement of the clutch release bearing as a preventative measure. This is always recommended, however it is sometimes necessary to fix this problem in some cases when a failed bearing is all that's broken.
A quick look at your manual transmission will show you the location of your clutch release bearing. It is always connected to a fork that moves it back and forth when the clutch pedal is pressed. Sometimes that fork is actuated by a hydraulic slave cylinder, and sometimes it is actuated by a cable. Either way, simply follow the cable or hose down to where the bell housing meets the transmission, and there you will find the throw-out bearing. The presence of this bearing is what makes it at all possible for the rotation of the flywheel to separate from the rotation of the transmission input shaft so that a gear shift can take place.
Working on your transmission can sometimes be a laborious task. Every engine is different, so the steps taken to undergo the installation of a clutch release bearing will vary from vehicle to vehicle. The basic steps are simple, however.