Vibrato is a technique of rapidly moving a note up and down in the direction of the adjacent strings. Vibrato is an important method of sustaining a note once it has been picked. It also gives much more expression to your playing.
Vibrato is usually found on long notes, or a note at the end of a phrase. Vibrato is usually obtained by the movement of the wrist away from the neck and back towards the neck, much like turning a doorknob. The symbol for vibrato is a wavy line.
The following lick demonstrates the use of vibrato.
Adding vibrato to a bent note is a great way to keep the note sustaining as well as giving a more emotional quality to the music. When practicing this type of vibrato, be sure to reach the highest pitch intended for the bend before releasing the pressure slightly.
Then increase the pressure again to return the note to its original bent pitch. Practice slowly at first and increase the speed gradually.
Here is a lick which uses vibrato on bent notes.
This one makes use of vibrato on bent and unbent notes.