Bending

Bending is a technique used to increase the pitch of a note by increasing the string tension. It involves pushing or pulling the string while maintaining contact with the fret, sliding the string up or down against the fret.

Half, Whole, and Other Bends

The two most common kinds of bends are half-bends and whole-bends. A half bend raises the pitch one half-step; a whole bend raises it one whole-step. Pretty simple, right? Beyond that there are as you'd expect: 1 1/2 bends, double bends, and 2 1/2 bends. 1 1/2 is usually as large as you'll ever see, but even that is rare compared to whole and half bends.

A special case is the 1/4 bend. This is common in blues playing - it bends the note halfway between the current note and the note one half-step higher. Since this pitch isn't inside the chromatic scale and playable on the guitar without bending, it's difficult to practice bending the note to exactly the right pitch. But generally, it's not worth worrying about - a 1/4 bend is almost never sustained but used to lead into another note. You start the bend a little late in the note duration and switch to the next note before actually reaching the 1/4 step pitch.

Pain

The first thing a beginner may notice is that bending hurts. Yeah, that's going to happen. A beginner usually doesn't have strong calusses on his finger-tips yet. Simply fretting the thinner strings may irritate the skin. The additional tension of a bend will surely hit some nerves. Just keep at it - within a short amount of time, your finger tips will toughen up, and you won't feel any pain at all.

Bend Up or Down?

Should you bend the string up towards the sky or down towards the ground? To some degree you will have to master both ways. The high and low E strings are too close to the edge of the fretboard to perform even a simple half-bend in that direction. So you're going to have to bend the high E upwards and the low E downwards. Otherwise, it's whatever is most comfortable to you. I find both ways about equally comfortable.

Some techniques, such as double-stops often bend one of the strings. If you are bending the lower string, you will need to bend upwards to avoid accidentally muting or otherwise interfering with the higher string note. And vice versa.

So practice both ways.

Adjacent Strings

You'll notice that your bend causes your fingers to come into contact with the adjacent string(s) to the one you are bending. This is fine. It only becomes a problem if you are accidentally fretting those strings and causing them to make too much noise. Generally, when you bend upwards, your finger begins to straighten, and the finger tip is rotating in a way that will pull the adjacent strings away from the fretboard. When you bend downwards, the opposite happens - your finger curls and hooks onto and pulls the adjacent string away from the fret. Pushing/pulling the adjacent string away is not necessary - it only suffices that you don't let the string(s) slide down your finger tip to the same point where your finger is fretting the bent string. Pushing them parallel to the fretboard is fine.

Reinforcement from Other Fingers

When bending with the middle, ring, and pinky fingers, you can use other fingers on that hand to help push the string, making sure you bend it all the way to the desired pitch. This really comes in handy for bends above a whole step. I use it on all my bends. Not only will it give you the extra strength necessary to do so as a beginner, but it will increase your control as a intermediate or pro player.

Notice this is not possible with the index finger - those are the hardest (and rarest) bends.