This is assuming that you're right-handed and are playing a right handed guitar. For lefties, you'll want to reverse this. Push on the front of the body of the guitar firmly with your right hand a bit below where you'd be plucking the strings. Simultaneously, leaving your left hand still fretting the note or chord you'd like to bend down, push forward gently with your left hand until the tones dip to the level desired and release. Now don't overdo this, there's a chance that it might break your guitar's neck. Oh yeah, and this does not work well with an acoustic guitar.