Clutch must be depressed on most modern cars or it won’t start, though it’s technically not required if in neutral. And best to depress the brake pedal as well, again, many modern cars won’t even start if you don’t.

And although it doesn’t matter what gear the shifter is in when the clutch is depressed, put it in neutral, so that if you accidentally let off the clutch after starting it, you don’t move, grind gears, or lurch and stall which puts strain on the gearbox and brakes. I’ve done that many times before I started checking the shifter first. Many people put the shifter in first gear when parked as an engine brake in case the parking brake fails.