ProPhoto galleries are created as custom post types, much like regular posts and pages. Accordingly, they get their own top level WordPress menu item, right above the ProPhoto link.
Functionally what this means is that Galleries exist all on their own and have their own unique permalink that you can customize. In WordPress terminology they are a custom post type. If you go directly to a gallery’s unique permalink, you’ll see the gallery along with the assigned layout. Galleries can be inserted into any layout, post or page.
The workflow for galleries is to create the gallery and then add/insert it. In the Visual Builder galleries are inserted into the active layout as gallery modules or selected as block backgrounds. When in a post or page, you can create and insert a gallery right there or insert a previously created one from the ProPhoto dropdown.
Much like fonts, ProPhoto has “styles” that are created for your galleries. A style is chosen for every gallery.