What's WordPress ?

WordPress is a free and open-source CMS based on PHP and MySQL. Features include a plugin architecture and a template system. WordPress is responsible for 22% of new U.S registered domains.

WordPress Structure

WordPress has basically three folders: wp-admin, wp-content and wp-includes.

/wp-admin - Admin Panel code – *read-only*
/wp-content
    /plugins
    /themes
    /uploads
/wp-includes - Common files. WordPress core files. – *read-only*

We should never change any line of code in wp-admin and wp-includes folders. There are many considerations about wp-content folder, but we will talk about it in child themes and plugins development section.