Forms you create with the Gravity Forms Plugin can use PayPal or Stripe to process online payments. 

To edit the settings, go to Forms, hover below a form, then the Settings option of the tools that appear, and click on PayPal or Stripe (note: Stripe needs to be connected first in your general Forms Settings, and must have a Stripe Credit Card field added to the form if you are not using Stripe Checkout). 

Click Edit below a PayPal or Stripe feed, or Add New to create a new PayPal or Stripe feed.

This takes you to the Feed Settings screen, where you can name the feed, connect it to an Email that has an associated PayPal or Stripe account, and manage other features.