You can add a page password to your website.
To do this, go to page settings on the menu page of your website.
Go down to where it says page password and simply create a password.
This will now make that specific page restricted to viewing by only users who enter the password.
Please note that the layout of this page can be changed to suit your website and is available on any Plus Plan. Contact us at firstname.lastname@example.org to setup your own branded password page.