Jet Reports adds the Jet ribbon to Excel but makes no modification to Dynamics NAV. So, if you are not already familiar with the structure of NAV, you can use the NAV tools that you already know.
First, find the NAV information that you want to report on, and then open Zoom from the Tools menu. NAV will display the name of the table that information is in, as well as all the fields associated with that table.
For example, here is the Zoom for the Customer table: