Classes that build customizer pages, settings pages and meta boxes in posts.
Place the admin classes directory in your WordPress theme. Include the class files in your functions.php file:
// This is the functions.php file
// Of course be sure to update the paths so that they're correct
require( get_template_directory() . '/admin-classes/class-meta-boxes.php' );
require( get_template_directory() . '/admin-classes/class-customizer.php' );
require( get_template_directory() . '/admin-classes/class-settings.php' );
From here, each class is used in a specific way with a structured array of data.