1. Have a purchase order open for this vendor first. Purchase orders exist on QuickBooks Online Plus and Advanced. If you haven't created one for this order yet, do that before receiving anything; the receiving step works by pulling items off an open PO, not by entering them from scratch.
2. Start an Expense, Check, or Bill, whichever matches how you're paying. Click + New and choose whichever of the three fits: a Bill if you're not paying yet and the vendor invoices you, an Expense or Check if you're paying on the spot.
3. Pick the vendor. Selecting the vendor from the Payee dropdown surfaces any open purchase orders for them in a panel on the right side of the screen.
4. Add the purchase order. Click Add next to the correct PO. QuickBooks pulls every line item from it into the transaction automatically, with the full ordered quantity pre-filled.
5. Adjust the quantity to what actually arrived. If the full order showed up, leave the quantities as they are. If it's a partial shipment, lower each line's quantity to what you're actually receiving right now; QuickBooks tracks the difference and leaves the rest of the PO open for the next shipment or the final bill.
6. Save. Quantity on hand updates immediately for whatever you just entered as received. The PO's status updates too, showing partially received or closed depending on whether anything's still outstanding.