Hi @gmartinucci. Thanks for your message!
Currently with this plugin you could integrate subscription to SendFox via: WordPress user registration form, WordPress comment form, WooCommerce Checkout form.
You could make it an implicit subscription, where they get added to your list automatically, or make it an explicit one, where they need to tick the checkbox to get subscribed.
If you want to create an opt-in form to collect emails from any other place, you need to use the built-in Form Builder inside your SendFox account:
https://sendfox.com/dashboard/forms/create
Cheers,
Bogdan