The potential buyer's ability to change the design of the site

Hey. I’m very unfamiliar with WordPress, but would like to do sales on Themeforest. And now I’m limited only by a lack of understanding of how to make the buyer can change the items on the site. Customize the site to your needs, change colors, change fonts, add (written by me) shortcodes and more.

I’ve been creating websites to order all my life and I’ve rarely used CMS. So not familiar with that. Could you please guide me on the right path? How do I make such features to the user so that he can edit (visually) the site on their own? What should I use?

Check this:

Thank you very much, but I think it’s easier to use ready-made visual editors and page builders. Simply integrate the editor in your theme. Is it?