A Published page means it is accessible publicly to the world to anyone that knows the URL. By default when you sign up your page is published. Click "View public page" in the left hand nav to see what it looks like.
A published page means:
Anyone in the world can see it at [company-name].launchnotes.io
Your Public Releases will appear on this page when in progress or complete
People will be able to publicly create subscriptions to your LaunchNotes page
If you Un-publish a page it will no longer be publicly available. In this case, only signed in Team member and Internal Followers will be able to view and subscribe to Releases.