Believe it or not, no formal “publishing” action is required for you to make your page LIVE -- your event is live the moment you share its URL or send out your first invitation.
Worried about it getting out there prematurely? You don’t have to be. Your event will not be readily findable via search engine, and someone would need ESP or to be a preternaturally adept guesser in order to discover its URL.
If you do want to make your page extra secure, though, just click the little Settings Icon in the toolbar (it’s the little gear), and lock your page off with an access code.