Fuel has four constants in the global namespace to direct you to important directories. Fuel uses them internally to locate classes and other files. These constants are set in public/index.php.

Note: When you move any of fuel's prime folders (app, core, public, packages) be sure to update your index.php to direct fuel to the right paths.

Key Description
APPPATH Path to the application directory (/path/to/fuel/app). This is where your application directories and code reside.
COREPATH Path to the core directory (/path/to/fuel/core). This is where all the Fuel classes live.
DOCROOT Path to the location where the 'startup script' is. For your web application, path to the public directory (/path/to/public). This is where index.php resides. Everything accessible to user lives and is accessible via the browser. For oil command, path to where oil command resides.
PKGPATH Path to the packages directory (/path/to/fuel/packages). This is where your packages are installed (when installed through oil).
VENDORPATH Path to the composer root directory (/path/to/fuel/vendor). This is where your composer installs the libraries downloaded from

Note: When you use the Oil package, you have to make the same changes in the 'oil' file in the docroot of your website.

Note: When you want to run unit tests, you have to make the same changes in the 'phpunit.xml' file in the fuelphp core folder.