check out the tutorials...i think it is under "advanced techniques" or something like that. It is relatively easy to pick up the technique, it's recognizing when you can use it and getting your timing down that is really hard (at least for me). Hammer ons and Pull offs are just when you are holding a fret button down and strum on a note, and their is another quick note after that, you can release the original fret button and hit the other fret button without strumming and it will still play the note. example: there is a blue note followed immediately by a yellow note, strum on the blue then quickly let off the blue and press on the yellow without strumming and it should play. I think the notes have to be the ones right next to each other for it to work, but I'm not sure. The tutorial will explain it a lot clearer than I just did, so run through that and practice it some.