Create Empty Folder and name it i.e., e.g., plugin
Open it in Visual Studio or other IDE
create composer.json file in main directory
create another folder in main directory and name it "src".
create custom classes in "src" folder.
use namespace as "App" i.e., e.g., namesapce App\Controller
Run composer init command and enter the minimum required fields, after that register namespace in composer.json as e.g., { "autoload" : { "psr-4" : { "App\" : "src/" } } }
run command composer dump-autoload -0
create index.php file in main directory
paste require_once realpath("vendor/autoload.php") in index.php
Now You can call all the controllers functions there