Exposure

Knowing how to use the tools on your camera, and the tricks of lighting, will help make your pictures much more defined, showing what you want how you want it.
With modern digital cameras, most of knowing exposure is simplified to reading the histogram on it. Think of it as a compass or looking down the sights on a rifle that can think for you. It is a chart that automatically tells you if all of what you are looking at is being included in your picture. You can adjust the aperture (opening size in front of the lens), or the shutter speed (how fast the picture is taken) until the histogram shows that you have the exposure you want.
Light meters on the camera record lighting for your image, but in very light or dark fields they get confused and make it gray. In this situation you may want to change to another mode;

1.Evaluative/Matrix Metering
general purpose- usually used as default setting
2.Average Metering
Evaluative is better. Don't bother
3.Spot Metering
spotlights one area of picture. Good for wildlife
4.Center-Weighted Metering
emphasizes central 75% of picture. will not use very often


You can control the amount of light in your picture by adjusting time (shutter speed) and intensity (aperture).
exposure modes;
1. Aperture Priority (AV) Mode
gives depth of field. landscape=small, wildlife=big
2.Shutter Priority (TV) Mode
allows you to choose the speed and leave the rest to the camera. not used often
3.Manual Mode
Do everything yourself. useful in landscapes or extremely light or dark scenes.

In said light or dark situations, press the Exposure Compensation button.
Using variations of metering with the histogram aide in difficult shots such as backlighting, white light scenes, sunrises/sunsets, or very dark scenes.