First, you will need to click on the tabs near the top of the page and click on the settings cog and select
Add a new page.
Once the page has been created you can find this on your site and hover over this section and then click on the blue cog near the bottom of the page and this will open more options:
You can then select the
Settings option:
From here, you can select the
Show more Options section and this will give you more options for this page, one of the options being
Display this page
which you can turn off and this will hide that page. You can also select the
Display this page option from just above
Show more Options.
On this page, you can also create a password for that page and then save the changes. When someone clicks your secret page, they will then be prompted for a password to view it: