Adding the stock value to your products
The stock value can only be added to already existing products. See the guide about creating products here. When you have a finished product, go to Store > Products and select a product you wish to add stock value to. Note that stock value is set to unlimited by default. When you set the stock value to 0, it means that the product is out of stock and cannot be purchased.
You can keep track of your available and booked products in the products view. If the number of products in stock is positive, it will decrease automatically with each successfully paid and dispatched the order. When it hits 0, the product is essentially out of stock and cannot be purchased. If the stock value is not set, our system does not automatically change it with new orders.
Inventory management with product variants
When your product has variants, then you can manage its stock values separately. In the product's detailed view, find the list of variants and click on the variant you wish to manage. Now that variant's stock field is shown.