The clutch switch, located at the top of the clutch pedal, prevents the engine from starting when the pedal is not depressed. The switch, which is part of the starter circuit, is normally open. When the clutch pedal is depressed, it presses on a small pusher in the switch, completes the circuit and turns on the starter.
If the car engine starts without depressing the clutch pedal, the switch is either defective or not adjusted correctly. To check its operation, disconnect the electrical connector and connect an ohmmeter to the connector terminals. The circuit must not be closed when the pedal is released (pedal up) and closed when the pedal is depressed. If the switch does not work this way, try adjusting it. If it fails, replace it.