purchase order

[newbie]

hi all, I was looking for documentation on modules in Dynamics AX. I have read the book by steen anderson .Im finding it hard to find any documentation on flow of processes in Dynamics. e.g what procedures and flows are invloved in sales ledger.To give an example, I was trying to put a new field on a report in Purchase module. Now I dont know the tables invloved to get the field. It goes through so many tables and processes that i get confused. Hope you understanding my issue.Any links to read more bout flow and processes involved in sales and purchase modules etc. Thanks