Ok Creating pinch harms on thicker strings are harder. I use overdrive to get this effect cause it's easier. It is just the very edge of the thumb catching the string. You'll do it once quite by accident and keep doing it there after cause of the way you hold the pick and attack the strings. As for the other thing. I think you are talking about double stopping. This is where you finger of your left hand covers 2 strings and they are played together like a 2 note chord. A very effective blues method which i employ and that is easy to do but needs to be used sparingfly in solo playing otherwise it can sound very robotic. For both methods it's more to do with Soul than technique so keep practising and you'll get it down to a fine art.