If you installed the latest version of drupal9 it will have the following directories. compare to other versions of Drupal, drupal9 does not have a libraries folder
- /core contain all the files provided by a core that don't have an explicit reason to be in the / directory.
- /modules are the directory into which all custom and contributed modules go.
This directory contains the contrib and custom sub-directories, which can be used to make it easier to keep track of the modules.
- /profiles All contributed and custom installation profiles.
- /themes contain contributed and custom (sub)themes.
- /sites is the directory used for running Drupal multi-site setups and it's used in the same way as in Drupal 7. Modules and themes in /sites/all/modules and /sites/all/themes will override the ones in the base modules and themes directories. Modules in /sites/SITENAME/modules and /sites/SITENAME/themes will override others for the given site.
- /vendor is the directory where Composer dependencies go, for example, Symfony and Twig
Core Folder Directories
In addition, the folder structure in the /core directory has changed as well.
- /core/assets - Various external libraries used by core (includes jQuery, underscore, modernizer, etc.).
- /core/includes - Base-level functionality that Drupal uses through other /core folders.
- /core/lib - Drupal core classes.
- /core/misc - Frontend code that Drupal core depends on.
- /core/modules - Drupal's core modules.
- /core/profiles - Drupal's core installation profiles. These are Minimal, Standard, Testing and Testing multilingual installation profiles.
- /core/scripts - Various command line interface (CLI) scripts, mostly used by developers.
- /core/tests - Drupal core tests.
- /core/themes - Drupal core themes.
Composer Build Directories
When using composer to download and manage your Drupal project, Drupal core, and base level directories will be adjacent to a vendor directory.
/vendor - Various external composer PHP packages.
/web - parent directory for the above base-level and core directories.