Two handed tapping was popularized initially by Eddie Van Halen, who caught on, and was used by a lot of different guitar players, including yours truly. I try not to use it too much, because it has become somewhat of a cliché, but you can do some really cool stuff with it.
I want to start by looking at a lick loosely based on a piece by a former teacher of mine, Joe Satriani. And this type of lick involves playing a power chord. Right? So it's all tapped. So with my left hand, I'm tapping the bottom two notes. I'm doing the same thing, but just reversed, an octave higher. So everything is tapped.
The lick from Eddie Van Halen's, "Eruption," which is basically taking a triad and hammering on all the notes, and then pulling off with the right hand.
So once you're doing that, you have a lot of possibilities. You can shift your whole hand to the left. See what happens.
I can lower the bottom note.
And now I can lower the top. You know you can do any sort of pattern with it.
So I'm going to play what I just played, with full volume.