www.wysiwygwebbuilder.com

Hello!
Please tell me how to make nested pages in the program:
In the site manager, I made a "success" page, which is nested in the "subscription" page - http://joxi.ru/L21PRXoT0k1XWm

I need the "success" page to open at: ... subscription/success.php - http://joxi.ru/LmG1j5MflOP4aA
But now it opens at ... /success - http://joxi.ru/brRWYQZcOqPQ1m

And another question. Can I hide page file extensions from the site url? That is, I want to hide extensions - php, html

You have created a child page, this does not affect the structure of the published website.
You will need to use folders instead.
https://wysiwygwebbuilder.com/site_manager.html

To hide page extensions in the URL you will need to edit .htaccess on the server.
To hide page extensions in navigation go to Tools->Options->Publish-> Hide file extensions.
Please read the help before enabling this option!

Thank you very much for your detailed answer.
Problem solved