This plugin adding users making payment for your form to the ACYMailing mailing lists you want. And later, you can use ACYMailing to send newsletters to these users if needed.
To use this feature, go to System -> Plugins, find and enable Payment Form - AcyMailing plugin. Now, when you add, edit a form, you will see a new tab called AcyMailing Settings. Here, you can select the mailing lists you want and when users make payment using the form, they will be subscribed to these selected mailing lists.
