The four kinds of cost
Product costs
What each product cost you to buy.
Shipping
What fulfilment costs, per order.
Transaction fees
What your payment processor takes.
Product catalog
The products these costs attach to.
Where to start
Product costs first. They are the largest of the lists and the one that decides whether gross profit can be stated at all — without them there is no margin to report, whatever else you enter. Shipping and transaction fees are quick by comparison: most stores need one fallback rule for each.Related
Products report
Where per-product profit shows up once costs are in.