Can't figure out how to get API info from PayPal.

1. I want to set up PayPal to accept payments with the Classifieds plugin, but the "instructions" page that I'm pointed to is WAY over my head. And I can't find where to request an API in PayPal.

2. As the blog admin, I would like to be able to post classifieds to my own website at no cost, but the plugin indicates that it's not possible to have both free and paid classifieds. Is there a way around this for me?