The frequency dashboard consist of four frequency chart components that show you how frequent particular values for certain metrics are. They divide the range of possible metric values in a number of intervals and for each interval they show the percentage of the shots for which the metric value falls in the interval. This gives you quick insight in the expected values for your shots and the expected variation of that value. You can select the shots for which you want to see the charts in the selection bar.
Note that you can always change the frequency dashboard if you prefer other component. For this, use the edit icon in the toolbar. You can also change the settings of each component to change the information shown and the look.