Greetings!!!

I'm new to this board, and I'm really glad I found it...You guys are awesome!!!

I have a question on a technique I saw performed by Eddie Van Halen...

What he does is hammer on's....and uses the volume knob to control the tone...however I'm not quite clear how this is done...can anyone explain this to me??? Also, does anyone know where I can find the tab of what he plays, once I figure this out???

Thanks for the infor

X!