4a01b965_s___The_Basic_Guitar_Procedure__How_to
[Technique] Bend [How to] 
Play the first note, then bend the string with the playing finger (helped eventually by the other fingers) until you hear the next note (in the tab example, a whole step bend, from E to F#). There are also 1/2, 1 1/2, 2 steps bends.
Guitar Techniques - The Basic Guitar Procedure
How to