Hi there, @scott76. 

The PO will show up where that item receipt came from. Purchase Order is a non-posting transaction, you can create a new one if you want the PO to exist as a memo type. You need to create a bill first so you can make a payment. When you create a purchase order you can link it to a bill.

If your vendor paid 50% of the purchase, you can make a payment from the bill and modify the line item having the 50% payment. To pay the remainder, you can go back to the bill and create a payment again. 

Here's an article that you can read through about purchase orders.

Don't hesitate to comment anytime if you have other questions.