cstack on "[Plugin: Form Maker] Understanding Paypal options"

Hello. I don't really understand the Paypal feature too well. My objective is to charge the end user a percentage of the product I am selling which I'll have stored in the DB. So I need a dynamic amount instead of my current 100 dollars. I just tried the Paypal radio buttons but I don't see where to set it to do anything other than display what I have in the db. Any help would be awesome help I thank you.
Casey

https://wordpress.org/plugins/form-maker/