Only modify wp-content/ — never touch wp-admin/ or wp-includes/ as they are overwritten on updates.
WordPress File Structure
wordpress/
|-- wp-admin/ # Admin dashboard (never modify)
|-- wp-content/ # YOUR customisations
| |-- themes/ # Installed themes
| | |-- my-custom-theme/
| |-- plugins/ # Installed plugins
| |-- uploads/ # Media files
| |-- mu-plugins/ # Must-use plugins (always active)
|-- wp-includes/ # Core WordPress code (never modify)
|-- wp-config.php # DB config, secrets
|-- .htaccess # URL rewriting
# Golden rule: ONLY edit wp-content/
# wp-admin/ and wp-includes/ are overwritten on every update