Hey Vanina,
Thank you for reaching out to us!
The Events Calendar (TEC), Events Calendar Pro (ECP) and Event Tickets Plus (ETP) are completely different plugins with different functionalities:
The first one (TEC) creates the calendar in your site, the second one (ECP) add some extra functionalities to your calendar like recurring events, geolocation and advanced widgets. The last one, Event Tickets Plus, allows you to add tickets to a given event and sell those tickets entirely within your site.
So answering your question, installing and enabling Event Tickets Plus won’t affect your calendar (it would work the same way as it is working today).
Let me know if you have any other questions and I’ll be happy to assist!
Regards,
Patricia