In the reports sub-menu you can find out everything about your shop. The reports contain all the data that you have provided the system with, they process them and then the reports apps present you all the data in a very understandable way.
The info that you get is invaluable as you can get great answers by filtering the data by date. All the reports can be exported to popular data types such as CSV, EXCEL and XML so that you can use them with 3rd party apps aswell.
There are many sub-reports depending on the analysis you want.