If you want to present drafts of your story within a team or keep content exclusive, you can easily protect published Pageflows with a password. 

To protect a story click on “Publish” in the editor sidebar:

Select whether you want to publish the story indefinitely or only until a certain time and activate the "Protect with Password" checkbox. Readers visiting your story will be prompted to enter the displayed user name and password. Pageflow suggests an auto-generated password. You can edit it freely if you want a password that is easier to remember.

The dialog displayed to visitors of your story looks different depending on the browser:

Once you are ready to make your story publicly available, use the same workflow to publish it again - only this time make sure the "Protect with password" option is no longer checked. You can also password protect a story that already has been published without a password. Public access is then no longer possible.