framework:
    ...
    log:
        handler: '%env(default_logger)%'.%kernel.environment%

use Psr\Log\LoggerInterface;

class MyController
{
    public function __construct(LoggerInterface $logger)
    {
        $logger->info('This is an informational message.');
    }
}

return [
    'default' => env('LOG_CHANNEL', 'stack'),

    'channels' => [
        // ...
    ],
];

use Illuminate\Support\Facades\Log;

Log::info('This is an informational message.');

use Monolog\Logger;

class AuthenticationController
{
    public function login(Request $request)
    {
        // ...

        Logger::info('User {user_name} logged in at {date_time}.', [
            'user_name' => $request->input('user_name'),
            'date_time' => Carbon::now()
        ]);
    }
}