In some digital cameras and in every DSLR, with exposure compensation, you can over or underexpose the sensor in third, half, two or three stops.
+1 increases the amount of light by one stop
-1 decreases the amount of light by one stop
It is most effective when used with centre-weighted or spot metering
Tip #1 - It's better to take the photo underexposed. You can bring back details in the shadows, but you can’t get back details in the highlights if they are blown out.
How to: determine the exposure of
Light
cloud and overcast: reduce shutter speed, increase the aperture.
bright and sunny: fast shutter speed, small aperture
Moving Subject: increase shutter speed, unless want blur
Greater depth of field: small aperture
Here a gallery of photos of a lovely family, in Melbourne, where I used the exposure compensation in camera, instead of changing aperture or shutter speed.