Many cameras can display histograms.
A histogram is a graph of how many pixels there are at different brightness levels.
The bottom axis is brightness.
The shadows are to the left; highlights are to the right.
The left axis is the quantity of pixels at each brightness level.
Here's the histogram for the photograph of the white hydrangea flowers on sunny day.
The dark corner on the right side of the photograph is to the left on the histogram.
The leaf pixels are in the middle, as they have a medium brightness.
The flower pixels that are in the sun are to the right.
Here's the histogram for the eggs taken on an overcast day.
Because the scene is has a medium to medium-high brightness, the graph is taller in the middle and to the right.
Here's a histogram of black velvet.
Because the fabric is so dark, the graph is tall on the far left side.
How can you use histograms?