The Beaver Builder theme isn’t required for the Beaver Builder plugin, and some licensed versions don’t include it, but it’s a great basic theme with good code and lots of options that can be set in the WordPress Customizer.
Whenever you use a theme, you should use a child theme version of it as the active theme, so any customizations you make don’t get overwritten by new versions of the parent theme.
All Beaver Builder theme customization is done through the WordPress Customizer, which you can access by choosing Appearance > Customize on the WordPress Admin Panel. Here are a few of the things you can customize with a Beaver Builder theme:
Color scheme
Default fonts for headings and text
Site header and footer layout and content
Menus and widgets
Custom global code for your site