The supplier dropped off a case I never ordered and I want to keep it. How do I get it onto the shelf?

Write it its own purchase order. On Menu → Purchase orders create a new order for that supplier with just that line, the quantity and the price on the invoice. Mark it as sent, then receive it straight away. Receiving is the step that puts goods on the shelf and moves the ingredient's average cost, so the case is now counted and priced like everything else. If you do not care about the cost and only want the number right, the Stock-take panel on Ingredients & suppliers is the quicker route: type the new total beside the ingredient and press Save the count. Either way the movement is written under What moved at the bottom of the page.