The product page formats function in much the same way as the Gallery Formats. For each non-print product, you can choose from several different layout options to display your products in different organizational structure.
This mostly comes into play when you have a hierarchy of nested products, for example a main Calendars category item, with several sub-product Calendar products nested underneath. You have different options for displaying those calendar products on the main calendar page.
Since the product format behave so similar to the gallery formats, please consult the Gallery Formats help page for more info about how the different formats work.
And, as always, don't be afraid to experiment for yourself to see what the various formats look like on your live website. That's the best way to learn. You can always change them back.