The two cycles every business runs — procure to pay and order to cash — as D365 models them, including matching policies, pricing and discounts, agreements, charges, and what changes when two of your own legal entities trade with each other.
Every business runs two cycles. It buys things and pays for them, and it sells things and gets paid. Almost everything else in an ERP exists to support, record or account for those two loops.
The requisition is worth a moment. It separates asking from committing, which lets approval happen against an internal request before anybody has told a vendor anything. Businesses that skip requisitions and approve purchase orders instead are approving a document that has already been sent.
The packing slip is the one that surprises people arriving from systems where only the invoice posts. Delivering goods is an economic event: the stock has gone and its cost is incurred, even though revenue has not yet been recognised. The packing slip records exactly that, and the invoice completes it.
This is where most implementations underestimate the work, because pricing in older systems is usually a lookup with special cases bolted on, and the special cases are where the real business logic lives.
A purchase agreement is the blanket order or call-off contract: a commitment to buy a quantity or value over a period, with orders released against it and the remaining commitment tracked. A sales agreement is the same on the selling side.
A charge is a cost that is not the price: freight, duty, insurance, handling, packing.
When both parties are legal entities in your own group, the movement is not a transfer. It is a sale by one and a purchase by the other.
Credit management holds credit limits, blocking rules and release workflow, so an order to a customer beyond their limit is stopped by configuration rather than by somebody remembering.
Both trading cycles work the way you already expect. What D365 changes is that the controls and the pricing logic become explicit configuration rather than implicit behaviour.