@ h.quinn

check your settings

gear>settings>company settings
sales>products & services
and turn on qty tracking (inventory)
and
in company settings>expenses>bills & expenses turn on the items table and purchase orders. 

When you enter an expense or bill, about half way down the left side is a title "item Details" click that and a table opens where you can select the item, qty and item total cost for purchasing inventory

then see the pic for a new inventory item set up