Here is a lesson on Tapping from Duncan Jones one of our resident online guitar tutors showing you how to tap on guitar. The technique uses left and right hand hammer on's and pull offs.
This technique will allow you to play fast and seamless legato lines, for arpeggios, scales and chords. Although at first made popular by Eddie Van Halen, the technique has evolved and can now be seen in acoustic guitar as well as rock.
Below are some basic ideas to get used to the technique.