How do you read a histogram?

[JasonMX]

I have been shooting with my Canon Digital Rebel, and usually shoot all pictures and do level correction in Photoshop. I was thinking that I should finally figure out how to use that "histogram" people talk of. I have used similiar things in statistics, so I think I get the idea.

Can anyone explain how to read it or post links to sites with information on it? Thanks!

[HJMinard]

The histogram is invaluable ... probably the biggest advantage of digital photography. A good explanation is located here (http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml).