From your event dashboard, go to "registration configuration" -> "stores"
From the Purchase Options for a product, select "View" under "Advanced Configuration"
In the "View purchase option" pop up window - you'll have the option to setup more details in the "Stock" section.
The 3 main options you might need to use are:
Per membership limitation: Maximum of product a single identity membership will be able to purchase
Per user limitation: Maximum of product a singly user account will be able to purchase
Required shipping: If that box is ticked, we will force the buyer to confirm their shipping address, can be very useful for a magazine subscription or any item you plan to ship.