it's like this. kinda like harmonics, but you have to move your hand from the first to the 12th or which ever fret it is. so press it like you want to do the harmonic on the 3rd fret and then pick the string and slide the hand to make harmonics on 4th, 5th, 6th ...12th fret.
you can put your whole finger, but i do it,and i saw edge do it, i put my point finger on three higher(e,b,g) strings, and my thumb on the three lower strings