Auto bracketing is an easy way to make sure that you get an accurate exposure in tricky lighting conditions. The camera automatically takes a sequence of 2 to 5 exposures with settings at, over and under the suggested exposure with a diffference of anywhere between 0.3 and 2.0 EV. Of course it is not necessary to bracket every shot you take. The trick is to recognize when your camera's meter might be fooled into a wrong exposure. This will happen in lighting situations where dark tones or light tones dominate the scene, or where the dynamic range is too large for the camera to record.
Take night time buildings lit by floodlight for instance. The contrast range between the spotlights and the dark sky will be quite high.This would be a perfect situation for a bracketing sequence. Take a couple of shots under and over what the meter suggests and see in which image the lit buildings and the surroundings are recorded best.
Not every camera has the possibility for auto bracketing, but if it has a manual mode it is easy to bracket exposures yourself. Set the meter's exposure on your camera and change shutter speeds or aperture by 1/2 to 1 stop for each image in the sequence.
Taking 2 images under and 2 over the suggested exposure is usually enough to ensure one perfect exposure of a scene.