In order to assign stock quantities to products, you'll need to enable stock management and assign a warehouse to the location associated with the/each product.
- Go to Settings in the left navigation bar. 
- Under BUSINESS, select Locations. 
- Press the edit icon to the right of the location. 
- Under CHOOSE WAREHOUSE, select the location of the warehouse. In most cases, the warehouse and the location are the same. 
- Press Save Changes. 
