Short: The controller sends it to the view.

Long: I assume you are using a freshly installed laravel project, which provides an authentication example out of the box. Now look at the AuthController (app/Http/Controllers/Auth), you will recognize that it uses a trait called AuthenticatesAndRegistersUsers where you'll find the following method:

public function postRegister(Request $request)
{
	$validator = $this->registrar->validator($request->all());

	if ($validator->fails())
	{
		$this->throwValidationException(
			$request, $validator
		);
	}

	$this->auth->login($this->registrar->create($request->all()));

	return redirect($this->redirectPath());
}

This is where all the 'magic' happens. I recommend to read the following documentations which will help you to understand this function:

• Passing data to views: http://laravel.com/docs/5.0/views
• How validation works: http://laravel.com/docs/5.0/validation
• And both combined - passing error data to views: http://laravel.com/docs/5.0/validation#error-messages-and-views

Regards MightyM