The main advantage of boxplots over stemplots and histograms is:.

The main advantage with boxplots (aka box and whisker plots) is that we can spot the five number summary very quickly. The five number summary consists of these items:

The min and max are the left-most and right-most tips of the whiskers, assuming there aren't any outliers. They are the smallest and largest items.

The left and right edges of the box represent Q1 and Q3 in that order. The vertical line inside the box is the median. The vertical line does not have to be at the exact center of the box.