Joomla! 2.5 User Groups permissions

Permissions to do things: Access Control

There are different levels of permissions for doing things in a Joomla! Web site. In particular there is a distinction between:-

Which users can gain access to what parts of the website? For example, will a given Menu Item be visible for a given user?

What actions a user can perform? For example, can a user edit or publish an article?

Users are grouped together in groups. In Joomla! 1.5 these groups give robust but fairly simple distinctions. It has a coarse granularity in that you cannot set permissions to small groups or individuals.

Front-end is the web site you can see. If you are an 'Author' - you can only edit pages that you have created. So if you look at the pages done by other people - you will be able to read them but there will not be an edit icon associated with the Article. However, the list below shows that Publishers and Editors can edit any article - which sounds easy but needs some care where there are a lot of people submitting content.

Back-end is the Administrators section of the Web site.
The following lists groups and associated permissions:-

Front-end Groups

These groups can only use the front-end of the website.

* Guest 

           Can view the parts of the Site that are not restricted to one of the other two groups.

* Registered 

           Guest Group privileges

           Can view Articles which have been given Registered Permissions

* Author 

           Registered Group privileges

           Create new articles but cannot publish articles

           Edit articles they own

           View special content

* Editor

           Author Group privileges

           Can edit all articles, even those that are not published

* Publisher 

           Editor Group privilegesCan publish articles

Back-end Groups

These groups allow you to log into the Administrator Back-end

* Manager
            Publisher Group privileges
            Can login to the Administrator Back-end
 * Administrator
            Manager Group privileges
            Can create new users
            Can install extensions
* Super-Administrator
           Administrator privileges
           Can change site template
           Can change global configuration

The permissions are allocated to usernames by the Administrator and managed through User Management interface in the Back-end of Joomla.

User permissions for a new site
You may not yet know enough about your new site to know how best to plan the management of users. The important ideas to carry forward into the next few documents on design of the content and menus is that:-
   - you may want an idea of how much of the site should be open to everyone to read
   - you may want to register all users, but limit them to be able to read the content without changing it.It is good to have some idea of whether some menus or Articles will need to be available to a restricted number of users.
   - you may want some users able to add content
   - you may want some users able to manage the content
   - you may want one or more users to manage the site

Source:  http://docs.joomla.org/How_permissions_work_in_Joomla!_2.5