wp-includes folder contains all the other PHP files and classes which is required for WordPress’ core operations. Again, you shouldn’t want to edit any files in this directory.
wp-admin folder contains the various files of the WordPress dashboard. You know that all administrative or functions related to WordPress, such as writing posts, moderating comments, installing plugins and themes are done via the WordPress dashboard. Again, you shouldn’t want to edit any files in this directory.
wp-content folder contains all user uploaded data and is again divided into four sub-folders: