The four most important reference files and folders in WordPress core are wp-config.php, wp-admin/admin.php, /wp-includes, and /wp-content/. The wp-config and wp-admin files include your database, localhost, admin user name, and password. They also determine which plugins and themes are running with the core distribution. The wp-includes and wp-content file contain your stored media resources and other system files. Users should avoid making any code changes to these resources on WordPress sites.