routing and controllers

[eluser]deineMudder[/eluser]
Hello,
sadly i got another basic question i guess, where i lack understanding of CI.

my actual controller folder looks like this

Code:

controllers
+ admin
  - user.php
  - navigation.php
  - article.php
  - roles.php
  - ....
- homepage.php

im trying to create a small CMS for a site and thought that structure for the administration part could be handy.

each controller (i.e. user.php) has the functions insert, edit, delete ...
as soon as i try to access those controllers hes trying to load a function of admin

controller (admin), function (user)
instead of subfolder (admin), controller (user), function (index)

anyone who could help a newbie to set it up correctly?