Hi,
Acymailing does not register attendees for your events, that's all handled from within Event Booking.
The Event Booking add-on offers you the possibility to easily add your events to your campaign or to filter your suscribers based on fields in Event Booking.
Acymailing will only send mails to subscribers registered in Acymailing.
Please, have a look at the documentation: https://docs.acymailing.com/addons/joomla-add-ons/event-booking. If you have any specific questions, please let us know.