When you make the event live, it means that the participants who have already been created in the event can access it.
There is three ways to make to event live:
1) You can click on the "Make the event live" button located on the top right corner of your screen.
2) You can activate "Make the event live" in your "Event settings."
3) When you send invitation e-mail, your event becomes automatically live.
It is possible to stop an event that is already live by going to "Event settings" and disable "make the event live." This way, your participants have no longer access to the event platform.