I would suggest to check the “Documentation”, “Blog” & “Download” section in order to gain understanding of NAV & ERP world.
In order to understand the financial term like “G/L, Sub Ledger, Setoff, Interim Account”, please download the Financial maunal. I am sure it will help you a lot.
In the same manner, manufacturing manual will help you to understand the manufacturing flow in Navision.
If you’re a customer then you can access all the training material for your version on CustomerSource and also the available manuals. But you also find a lot of manuals on MSDN.