The following is taken from the Joomla! Website, it will help you understand how you can control the users of your website. It explains the different levels of permission that you can give your visitors. And also the difference between the front-end and back-end of Joomla!

In order to understand the Joomla! Access Control List it is also necessary to consider the structure of a Joomla! web site as well.

Every Joomla! web site installation has two distinct access/content zones.

Front-end:

The first of these zones is the Front-end. Also known as the Public Front-End.

The Front-end is the web site that all visitors will see when they input the web site's URL address - whether this is on the Internet, or an Intranet, or a simple, local, standalone installation of Joomla!.

The Front-end includes the Front Page (home page) and is where all the web site Content Items, images, and the rest of the massive array of possible Content will be displayed and is accessible to the web site visitors.

Back-end:

The second zone is the Back-end. Also know as the Public Back-end, Administrator, Control Panel, and many other names.

The Back-end is the control room or flight deck of Joomla!. Here, all the software, functionality, and security of the Joomla! installation can be managed (in conjunction with the database and web server administration functions).

The Back-end is not available to public viewing. Normal visitors to the web site will not be able to view or access the settings or configuration of Joomla!.

To ensure that access to the two zones is kept separate Joomla! has two very separate classification levels of User Group that match these two zones. Within each classification level there are a number of User Groups.

In addition, there is a system for classifying the actual Content that each Group can view.

The following section on User Groups will clarify which User Group can access a particular Class of Content.