Left/Right handed systems

I never really understood why a left-handed system is, well, left-handed. I can get fingers to point in the same direction with both my hands.
Please enlighten me!

Move both of your hands upwards while twisting them in the natural direction (That is, inward).  These are left and right handed helices.

You're right; the one where you use your thumb and curl your fingers isn't really clear.

With your left hand, make a gun with your thumb (the first vector) and index finger (the second vector). Unless you can bend your fingers backwards, your remaining fingers will curl inwards. With an identical orientation on your right hand. "inwards" is the opposite direction.

>>1

doesn't that hurt?