Shipping price changes only apply to orders placed after you save the change — existing orders keep the price that was in force when they came in. VAT is set per item with the dropdowns in the table (default above applies until you change one). Fees: Shopify Payments orders use the actual fee recorded on the transaction; the rates here cover other providers. Everything saves to the store, so all users see the same numbers.
One row per order. Item price = unit price × quantity, per item. VAT is calculated per item on its price (item price × rate ÷ (100 + rate)). Cost price is for ONE unit (× quantity in the column): grey = filled from the product's "Cost per item" in Shopify and follows it; type your own figure (black) to fix the cost for that order — clear the box to go back to the product's cost. No cost anywhere counts as £0. Profit = order total (inc shipping) − VAT − payment fee − shipping cost − cost price, shown red when negative. Grey fee = estimated from your configured rate; black = the provider's actual recorded fee.