When you're just touching the string, that are [u]natural[/u] harmonics because you're deviding the string into several shorter strings of the same length, so the string sounds higher. (min 1 octave, when done on fret 12, there you devide the string in 2 string by half)

[u]Artificial[/u] harmonics are played just like normal notes. But the picking motion must be done so that the thumb, where you hold the plectrum, is touching the string shortly after the plectrum did.
It needs some practice to master it. Then you can play it with vibrato, bendings, etc..