How to use repositories properly

Im using laravel 5.4 and im trying to figure out for a new application how to set it up well. So i digged into repositories which didnt gave a real answer. I found http://ift.tt/1ZsSj2g and this sounds pretty clear to me.

A old co worker told me another way of using repositories but im taking his answer not really well... He showed me this:

class ExampleRepository
{
    public function __construct()
    {
        $this->models();
    }

    private function models()
    {
        $this->user = app( User::class );
    }

    public function findUser( $userId )
    {
        return $this->user->find( $userId );
    }
}

My real question: which example should i use according to standards and flexibility?