A distribution is the way a set of data values is spread out. A box plot is a quick way to show that spread on a number line. It uses the five-number summary: minimum, lower quartile $Q_1$, median, upper quartile $Q_3$, and maximum.

The whiskers run from the box to the minimum and maximum. The box goes from $Q_1$ to $Q_3$, and the line inside the box marks the median.

To measure spread, use $range=maximum-minimum$ and $IQR=Q_3-Q_1$. The IQR describes the middle 50% of the data, so it is often more useful than the range when comparing box plots.