The password page can be enabled when your store isn't ready to sell and you want to have a placeholder landing page in place instead. Here is information from the Shopify Help documentation about the password page. Note: some of the code edits suggested there are out of date and don't apply to the Whisk theme.
The password page comes with a simple header where you can upload your store logo, and a simple footer that displays links to log into your store as an admin or to visit the site by entering the password. You can choose to show social media links if you want here as well.
You can build the content on the password page with sections and blocks just like any other page in the theme! Just note that any section that shows products for sale may not look right, and won't work because the visitor will not be able to shop. These are the sections that will work well on this page:
Image grid with text
Image with text
Question and answer