The product page will show you the important information about the product you have selected. If the product is a publication then you will have Issues and Sections in the tabs below, if it is an exhibition you will have the Payment Schedule and Halls tabs instead.
The Main tab shows all of the main information about your product. Such as the default item type, default order type or any flags. You can also link the product to a product group, or create a new product group and link it. Do this by clicking the button on the far right hand side.