In the PO area it is currently not possible to input a line item and advise how many of that item you're ordering. Instead you have to input the item, then duplicate it as many times as you need. The only other option is to make a model that specifies it is more than one of that item, and that removes the accuracy in reporting (which also doesn't currently exist, but I'm hopeful will eventually).
As seen below, I ordered 20 items, 10 of 2 different types. On a normal invoice or PO it would simply show two lines for the two products, and have a column for price, a column for quantity, and a total that indicates how much you're paying for however many you bought. Not here unfortunately, and it's very cumbersome in large orders to stay accurate without having to click the plus sign over and over.