The purchase order is sent to the vendor/supplier to outline what the merchant would like to purchase and how much of it they would like to receive.
You can create a PO from the inventory > Stock Control > New stock movement, then select the purchase order from the list of the documents:
Further, you could add the items either from the catalog or any open order as follows:
After receiving the items from your vendor, navigate to the PO and select the “Receive items “ button to complete the purchase order: