The Mechanics of a Bend
For many players, bends are the unique part of guitar playing. While it's true that other instruments are capable of bending pitch, few have the variety of bends to rival the guitar.
A bend is performed by horizontally pushing a string. While any finger can bend a note, your third and fourth fingers are best suited for the job. Bending is a strength-in-numbers exercise; one finger has a much harder time bending a note than three fingers do. On guitar, the finger that plays the highest fret is the finger that sounds. You can place your other fingers behind any note you play to prove this; no matter what you do behind a note, the highest fret will sound. When you bend, the other fingers help you bend the note up. Using multiple fingers to bend is crucial to proper bending.
It looks pretty dramatic—you push the string far away from its usual position. This is normal. At first you may be afraid of breaking the string, but don't worry; guitar strings are made to be bent.
To get the most use out of your guitar, a proper setup is important. Improper string height, fret problems, and intonation problems can make playing the guitar harder to play and less enjoyable. Take your guitar to a qualified service technician every six months to ensure that your guitar is in top form.
The location of the note on the guitar is also important in a bend. The closer you are to the nut of the guitar, the harder it is to bend the string. The higher up the neck you go, the easier it is.
The guitar has the unique capability to play the exact same pitch (or note) on several different strings. If you have difficulty bending a particular note, finding that note somewhere else on the neck may make it easier to bend. The type of guitar you play will also affect how well you can bend. Electric guitars with light gauge strings will be much easier to bend on than an acoustic guitar with heavier gauge strings.