Set your inventory levels so that Clients can see if stock is running low, and customers cannot purchase an item that is out of stock.
From your Standard Fields tab within a Product, navigate to 'Inventory Control'.
Here, you can set your current stock levels.
Inventory Type - Currently "Global" or "None" are the only types available.
Display Type (when zero inventory) - This can be controlled on a per-Product basis. Use it to control what happens when a Product is out of stock; you can either hide the product from the shop or display it without accepting orders.
Quantity - Set the quantity you currently have in stock.