On more advanced digital cameras, you can check your exposure by using the histogram.
Note:Showing the histogram on the different cameras is done different ways - please refer to your user's manual to find out how its done on your particular camera.
Once you see the histogram, you can either adjust your aperture and/or shutter speed, or the exposure compensation to bring the histogram into line. (Again, refer to your user's manual to find out how to do this if you don't already know.) The right side of the histogram chart is the "highlight" side. The left side is the "shadow" side.
This is properly exposed image:
To make sure you have as much highlight detail as possible, the histogram bars should be as close to the right side (highlight side) of the histogram as possible without blocking up like this overexposed image:
If the image is underexposed like the image below, it can be rescued by lightening it in your editing program, but generally will gain noise (similar to grain in film photography.)