A Trill is a two notes repeated rapidly. You
can play a trill by combining the hammer-on and pull-off. This technique is used
a lot in heavy metal music. Try playing a trill, pluck the string once only.
Play string 1 downstroke, pressing with finger 1 in the fifth fret.
Hammer-on to string 1 with finger 3, on the seventh fret.
Pull-off finger 3. Repeat the hammer-on and pull-off several times
rapidly.