When you make the Event "live", it means that the Participants who have already been added to the Event can access it.
There are three ways to make your 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 an 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 toggle off Make the Event live. That way, Participants have access to the platform but no longer to that particular Event.