How to Read and Use Histograms

http://digital-photography-school.com/how-to-read-and-use-histograms/

"The histogram is a useful but often misunderstood tool that your camera provides to help you get the correct exposure on your images. In this article we’re going to look at how to read it and use it to your advantage to help you do just that.  Getting the best exposure (there is not such thing as the “correct” exposure, as it’s all subjective) in camera should be your goal every time you click the shutter. Using these tips should help you increase your success rate"

What can we learn from this histogram?

When the histogram tells you to adjust your exposure

What do the spikes up the sides mean?

One more handy thing on your camera – the “blinkies”

Also see: Exposing to the Right