First of all, the clutch is engaged by spring pressure. You have to push the clutch pedal to disengage the clutch.
When the clutch is disengaged, is is held there by the throwout bearing which is spinning. If the throwout bearing goes bad it will make noise while spinning. If it is severely damaged it may not push the clutch in far enough to fully disengage it.
Throwout bearings normally last a long time. They tend to wear out prematurely on people who rest their foot on the clutch pedal when the engine is running but not in gear, or when the slave cylinder travel is not correct (no freeplay).
If this is the problem, a new throwout bearing may be enough. Normally though, I would want to replace the pressure plate and slave cylinder too.
