No, I have not visual interface for add snippets I only see normal editor and I dont know the code for add… in the manual is there a button that click and you see the snippets but this button is not working.
You may want to open your own ticket for this since it’s a bit unrelated. If you click on the Fusion forum at the right and scroll down, you’ll see the new ticket form at the bottom of the page.
To answer some of your initial questions, if you just want to view the demos, I recommend doing so on the demo site we’ve setup ( http://fusion.themeluxe.com ). If you import multiple demos, you’ll get pieces from each. To undo everything, the easiest way is just to delete your database if you have no other content and start with a fresh WP install. But you can also just manually delete pages (make sure to also delete them from the trash) and delete widgets under Appearance->Widgets (probably why you’re seeing multiple footers).
The particle option is under the Customizer->Body, but this is also available under Page Settings on individual pages when you’re editing with Elementor.