Quote Originally Posted by wolivas
What does metering off mean?
Your camera has a built in meter that reads the light values available. You use it to achieve the best settings for the image.
Suppose your camera is set at iso 400. You set your aperture at f/8(for example). When you point at the brightest area it says you should use a shutter speed of 1/30" but when you point at the darker areas it will say 1 or 2 seconds. Change the iso or aperture and the shutter speed suggested will change also. You will generally have slow shutter speeds for night shots which is why a tripod is necessary.
Iso, aperture, and shutter speed all affect the exposure and they must be balanced to get a good image.