Here's a mind-picture for thinking of the engine and the clutch.
Imagine the engine as a lion, wild but trapped in a metal cage (under the bonnet). Turn the key and the lion wakes, but stays sleepy.
Pressing the gas is like stepping on the lion's tail ("adding fuel to the fire"). But the lion can start to bite only when you open the circus cage door. The clutch pedal controls that door. So open it gently. You can always close it again (by pressing the pedal a little) if you feel the lion's getting out of control. (You can also take your foot off its tail).
Here's an alternative reminder, with music.