Pages that have a password set can only be viewed when the password is entered.
You can activate password protection by going to the Pages section and clicking the Protect Page on the page you want to protect. This password will protect this page and all the subpages.
Passwords are ignored in the dashboard's live site preview, since you're the only one viewing it. Adding or removing a password will also add or remove it from all child pages of the set page.
You can also decide whether to have your navigate be visible even on protected page.
You can now set a timer on how long visitors can access your site before they need to enter the password again. You can do this on Options>Password Timeout.