If you sell items where you have a limited
number in stock, and where your resupply period might be more than a
day, you will normally want to use stock tracking to ensure you don't
sell items that you cannot deliver.
Stock tracking does not need to be activated globally for the store. Instead, you can apply just to the items that you need to track stock for.
When creating or editing a version, check the 'stock tracking' checkbox. There are two relevant text fields: the actual stock quantity, and the warn level.
When the stock quantity reaches the warn level or below, a stock warning will appear in the 'To Do' list on the right hand side of the back end. This way, you can re-order more stock before your supplies are exhausted.