There is ( or should be ) a switch on your brake pedal lever that tells your brake lights to come on. Could this switch be incorrectly mounted on your clutch pedal instead? Do you have a switch on each pedal? If you do the one on your clutch is so the car won't start unless the clutch is depressed. It might have the wires reversed or the switches might both be mounted on the wrong pedal.
Someone mounted the brake light switch on the wrong pedal?
For the brake it's pretty obvious. You don't want the brake to stay on when you aren't braking, so you need the spring to push it back. For the clutch it's the same but in reverse. You want the clutch to stay on, except for when you're depressing the lever. The spring keeps the clutch on, until you use the lever to overcome the spring. Then when you release the lever the spring kicks in again, engaging the clutch.
Either the machine does not "know" or the clutch/brake switch is bad. Either way it is a safety switch
Assuming you mean "engage the clutch" or "Release the clutch pedal" which is the exact opposite of what you actually asked: 1) clutch disc contaminated with grease/oil/brake fluid 2) engine misfire (is RPM high enough?)
1/2 inch, with 1-1/2 inches of free play in the clutch.
It uses brake fluid in the brake fluid reservoir. The clutch fluid (brake fluid) is fed by the brake fluid reservoir. The clutch fluid reservoir is just beneath the brake fluid reservoir. So, add fluid to the brake fluid reservoir to fill the clutch fluid, also.
Brake, emergency brake and the clutch
Either the drive belt is not releasing far enough when you press the clutch pedal or the brake is not engaging enough. You will need to see if the belt is still turning when you press the clutch pedal down.
You ONLY use the clutch brake when you're at a complete stop.
Yes, there is no such thing as clutch fluid. It's all brake fluid.
Brake Fluid Dot 3 Note: Brake and Clutch fluid are the same
The clutch does not use oil, it uses DOT3 brake fluid. The clutch cylinder gets its brake fluid from the brake cylinder and is directly below it. Add fluid to the master brake cyliinder reservoir.