1: On a page created with Google Page Creator
It is not possible to use pass word protection for a page completely created with Page Creator. I did some research on the internet, but all solutions involve inserting soem code into the HEAD of your page. Using the editor you do not have access to this part of the html code.
2: On a downloaded/uploaded page
When you download a page you have access to the complete code. Now you can insert your password protection in the HEAD of your page, save the file and upload it again. This way the first page of your site will be public, but all subsequent pages can be hidden from view.
This link will bring you to a page where you will find approx. 20 different ways for password protection.