When you receive items for which you have an open purchase order, you need to mark them received in QuickBooks and enter a bill to pay for them. From the Vendors menu, select Receive Items and Enter Bill.
In the Enter Bills window, select the appropriate vendor. A window stating that open purchase orders exist for this vendor will appear. Click Yes to receive against one of the open POs.
In the Open Purchase Orders window, check the correct PO and then OK.
Now you are back in the Enter Bills window in QuickBooks. Look at the Items tab and verify:
If there are additional taxes or shipping charges, click the expenses tab and enter them. Then verify that the amount due equals the amount of the bill and, assuming it does, save the bill.