You add to your inventory by purchasing new units. If you’ve negotiated a price with a vendor, you can create a purchase order assigned to the SKU you are purchasing.

In this example, we’re issuing a purchase order to buy 20 jackets.
When we invoice this purchase order, the jackets will be added to the inventory.

The invoice that is created for that purchase order is also posted to that inventory item:

When you post an invoice to inventory, a transfer into inventory is recorded for that SKU. The hotlink on the SKU label takes you to this record.

As this inventory is drawn down, the draws will be recorded in the lower half of the screen.