A purchase order records what you are buying from a vendor, in what quantity, at what cost, and into which location. Create one from Purchase Orders, add the products and quantities, and send it to the vendor. When the goods arrive, you receive against the PO and the units land in stock.

Receiving a PO line increases on-hand stock at the location and records a receipt movement. You can receive partially — log the 80 of 100 that arrived now and the rest later. The PO moves through draft, sent, partially received, and received as goods come in, and you are notified when a PO is fully received.