After you’ve added any assets, headers, text, call to action buttons, etc. to a portal, click Preview and you’ll be able to see how the portal will look for anyone you invite to or share it with. Continue making additions and changes to the portal in the Live Editor, then share it when you're done.
If you're unable to preview a portal, it may be expired. Choose a new expiration date or clear the current expiration to preview the portal.