The "Statistics - Number of open/closed tickets per ticketbox" report is a simple report that displays for each ticketbox, the number of tickets in their various states, namely closed (requires no attention), open (requires attention) and on hold (requires attention at a later time).
In the Workspace screen, expand the [Shared Items] node, click on [Report Center] and open the report [Statistics - Number of open/closed tickets per ticketbox], by double clicking on it.
The report will display the number of open, on hold & closed + total tickets for each ticketbox and its subfolder(s).