Adding password protection to a specific page or resource is easy. Here's how to do it:
From your dashboard, navigate to Publish > either Pages or Resources, depending on what you wish to password protect.
Find the page or resource you wish to protect, and click Edit.
Scroll all the way down to the bottom of the page, to where you see the Publish section.
Next to Visibility (with an eye icon), select Edit. Select the option for Password Protected. You will then be prompted to enter your desired password.
Click Update to finalize your changes!
If the page or resource you've just password protected is navigable from the front of your site, visitors will see this when they click on the page or resource: