When you have Inventory Control checked off on a product there are two places that you can set the inventory for that product depending on its other settings.
If you are NOT using the Variants feature, there will be a More Options screen available while editing the product that includes a field titled "Limit products sales to." Any number you enter here will be the stock for that product. Our cart will list the product as unavailable after the total sales reach that number, and you can change it at any time to reflect new stock coming in.
If you ARE using the Variants feature, the stock level of any given SKU is entered on the Variants screen directly.
There isn't a general screen to handle your inventory, any given inventory setting would have to be entered on the product itself.