Boxplot is considered an exploratory chart that lays out data into quartiles with minimum and maximum values shown at the ends of “whiskers”.  The whiskers are an indication of the variability of the data.  Longer the whiskers the more variable the data.  In the chart above, and with all categories on the x-axis, there is a 5 number summary including, minimum, first quartile, median (second quartile), third quartile, and the maximum.  

Like the bar chart this can be represented vertically or horizontally, this choice is mostly for readability and might vary based on the density of the categories or the amount of space available for the visualization.

From a layout perspective this chart is a lot like a bar with a numeric value on the Values (Y-Axis) and some dimensional data on the Category (X-Axis).  The additional data, in the above case, is Weekday and this shows the distribution of Sales across days of the week by Product Category.  

At a glance this chart type is great for understating the data variations and the median for a given category, but is more useful when each category or data point is examined. The tooltip is a key tool for finding these details and in the above example, additional related data is added to the tooltips. 

In general this is a great chart for the right data with the correct exploratory use case in mind.  If the goal is simple value comparisons on small amounts of data with limited variation than the complexities of this chart will just get in the way of the analysis.  For more explanation and details on a boxplot chart you can read this article.  If you want to learn more and play with Oracle Analytics check out this free course on Udemy – https://www.udemy.com/augmented-analytics/.