use of $route in routes.php

Well, I solved it, but I still don't know why. I just put index.php/ in front of the controller and now it works. I thought that I don't need to user index.php ? When I bring my app up from the chrome address bar I type "localhost/sub_crud", and that brings me directly to controller users and method login

Don't have an account? <a href="<?php echo base_url() ?>index.php/users/registration">Register here</a></p>

proof that an old dog can learn new tricks