The clutch cable connects the clutch pedal to the levers, which operate the clutch. These levers are responsible for engaging or disengaging the clutch and enable the driver to change gear.
Clutch cables can become subject to corrosion and suffer from constant wear and tear. If any fraying or other damage to the cable is discovered then you should immediately seek a replacement cable. When doing so you should only use high quality clutch cables for any car.