The inventory window lets you interact with your product list. You can define how many of each product you have in stock and at what point you will consider this product at low supply; you can also choose not to track inventory on a product-by-product basis.
In the inventory window, you will also be able to define a product's purchase ability; a product can be defined as purchasable on an online store, you can specify a product as coming soon and allow for pre-order, or a product can be selected as not purchasable online.
Stock - This is the specific amount of stock that you have for a particular product
Low Stock - An alert will be issued once the stock of the product reaches this amount
Purchasability - You have the option to make your product:
Available to purchase by anyone in your online store
Available for preorder with a “Coming Soon” status
Not have the product available to be purchased online, but can still be promoted as exclusive