Fast

Fast classes are the base classes to you FastFlight

FastController

It's the basic for a MVC Controller implementation.

namespace core\fast\FastController;

You can start your Controller right this way:
Go to path/to/your/project/app/controller/ and create a file YourController.php

namespace app\controller;
use core\fast\FastController;

class YourController extends FastController {

    public function index(){
        echo "Hello World";
    }
}

You'll need register a route

Go to path/to/your/project/route/ on the file web.php

Flight::route("GET /", [\app\controller\YourController::class, "index"]);

Or

use app\controller\YourController;

Flight::route("GET /", [YourController::class, "index"]);

See more aboute Routes in Flight Docs.