When you configure a buy route, you can purchase products in one of two ways. One of the ways to purchase this product would be to create a purchase order and add the product to the purchase order manually. This is the typical manual purchasing system, where a purchase agent perhaps uses other events outside Odoo or examines reports in Odoo to create purchase orders.
In addition to creating manual purchase orders, you can also create re-ordering rules that will automatically create draft purchase orders when the stock of the product dips below a set minimum. This method works well on products that are ordered frequently, and frees your purchasing managers from having to manually create purchase orders for some or even most ...