An example of how Vtiger CRM works?

Question

CRM

I'm trying to get into this CRM and simplify the process of taking orders and writing off his goods from the warehouse as much as possible. In fact, you need the following:
When adding a contact, see if he ordered before and what to
go in and add goods to him
Write off as many goods as orders
If there is an adequate manual or an example of this business process somewhere?