After enabling the Product menu, it will be visible on the portal. Under this menu, you can select the Price List and products. After selection, the portal user will get the “Create” button. After clicking on the button users will be able to select the object for which they want to create the product.
If Product is enabled for any object like Order and Opportunity, then you can add the Product object into the menu on the portal side.
After object selection, users will be redirected to the order details page. Here they have to fill the product details.