Exactly, think of it as a hose spigot, and your finger is the needle trying to plug the spigot. The bigger your finger, the less water that's gonna spray on the ground (as in a leaner needle), the smaller the finger, the more water that'll spray (as in a richer needle).
The needle opens and closes off the main jet, that's all it does, the taper, length, and diameter effect the transition from the pilot to the main, more or less.
Dunno if the helps explain it.