He strikes the open g string with his finger (to sound it) slightly, bar dives, then pulls his wammy bar toward the bridge and presses down (Same as pulling up your wammy bar...just a fancier way of doing it) then slightly touches the 5th fret harmonic. This produces that scream you hear.
I started learning guitar because of Randy Rhoads..but Yngwie J. Malmsteen is my biggest influence.