In Preferences > Forms you had the option to create custom forms for situations where you want to collect information from your visitor/buyer. As a review, forms can be used on a custom page, a checkout page, and also on a product page you assign in this area. You can add one form to a product page. Forms on product pages can not use the "File Upload" option for the form itself. Instead you should be using the File Upload option in Products > General Tab.
To add a form to a product page, go to: Admin > Sites > Choose a site > Catalog > Products > Choose a product, or create new > Forms Tab
A good use of a form on a product page would be in the situation where you may need to gather more information about a product that does not make sense to add to a pricing calculator engine, or any other option written into the product setup. An example could be a product that lets you choose the colors of the item when ordering. The buyer can choose how many they want and then check off the colors they want that you display in a form.
The form information gathered will display in the product summary the buyer see's after they place the order and in their order history. This information will also display in the order detail report you access in the order area of Admin.
Unlike Forms on custom pages, there is no form response or catpcha allowed.
Knowledge Base articles related to Forms on Product Page