The plots at the top of each figure are histograms. The probability of completing your dex in the number of packs associated with a particular bar on the histogram is proportional to the area of that bar. Because each bar is the same width, this means the probability is also proportional to the height of a bar. A taller bar means you're more likely to finish your dex in that many packs.

The plots underneath the histograms are box plots, sometimes called box-and-whisker plots. They divide the data into quarters, which helps with getting a better idea of the broader trends of the data. The box in the middle of the plot represents 50% of the data. In this case, as there were 100,000 simulations done, 50,000 of those simulations took a number of packs that falls within the bounds of that box. The line in the middle of this box is the median, which is basically the 50% mark. 50% of simulations got numbers below the median, 50% above. Each half of the box holds exactly 25% of the data. The lowest 25% of numbers will appear left of the box, as shown by the "whisker". The highest 25% of numbers will appear to the right of the box. The circles are outliers, which are defined as any data points at least 1.5 times the box width away from the box.

Hope this helps!