Now that you have some products in your shop, you need to make sure you are maintaining the inventory count for them. WooCommerce automatically removes counts for each order. You then have to manually add counts back as you replenish your stocks. You do have the option to select stock as strictly in stock or out of stock if you do not want to manage inventory counts to a specific number or amount.
As with my other introductions to WooCommerce, I will be teaching specific ways of managing WooCommerce. I recommend you to search WooCommerce Docs linked below for additional information.