The Statistics page in the Preferences window is where you can see information about your break usage, and see a chart showing your usage over time.
At the top of the window, page buttons enable you to switch between the Activity page and the Statistics page (as follows).
To the right of the page buttons, a Share button enables you to easily tweet, post, email, etc the statistics. Tell your friends how well you're doing!
Below the buttons is displayed the total number of times you have postponed, skipped, and done all breaks (or a specific one; see below). Plus the total duration of the breaks. These totals are since installing version 2.4 (or later).
A couple of pop-up menus enable you to choose what to display in the chart: the daily count for breaks postponed, skipped, or done, or the daily total duration. Plus whether to show all breaks, or just a specific one (which also affects the numbers above).
Finally, a line chart displays the totals for each day, using those options. If the All Breaks option is chosen, the chart shows stacked lines.
Hover over a diamond marker on the line to see a tooltip with the corresponding value.