Joomla is one of the highly rated CMS all over the world now.Many people like to have blogs and many like websites. The part of people who make the blogs always have a great doubt. And the question is how to assign special privileges to a registered member or members. Many experiments were done,but all of that failed. Atlast,the solution was here.
There are 2 ways to do it.First check,which system you are using for user registration. There are 2 ways,i.e,JOOMLA DEFAULT LOGIN MODE AND COMMUNITY BUILDER LOGIN MODE.
Community builder is one of most highly rated award winning Joomla component.
There are four (4) Front-end groups available:.............

Registered - This group allows the user to login to the Frontend interface. Registered users can't contribute content, but this may allow them access to other areas, like a forum or download section if your site has one.

Author - This group allows a user to post content, usually via a link in the User Menu. They can submit new content, select options to show the item on the front page and select dates for publishing but they cannot directly publish any content.

Editor - This group allows a user to post and edit any (not just their own) content item from the Frontend. They can also edit content that has not been published.

Publisher - This group allows a user to post, edit and publish any (not just their own) content item from the Front-end. Publishers can review all articles, edit and change publishing options but the can also determine when an article is ready for publication, making it visible to Registered, Author and the Unregistered members.

There are three (3) Administration section groups that allow access to Joomla:

Manager - This group allows access to content creation and other system information from the Backend. Think of Manager users as Publishers, with Backend access. They can log in through the Administrator interface, but their rights and access are generally restricted to content management.

Administrator - This group allows access to most administration functions. An Administrator user has all the privileges on the back end of a Manager, but they also have access to set options on, and install/delete components, modules and bots, User Manager access and can view the site statistics.

Super Administrator - This group allows access to all administration functions. Only another Super Administrator can create or edit a Super Administrator user account. Full access to ALL AREAS is given to Super Administrators, and once created they cannot be deleted – EVEN BY ANOTHER SUPER ADMIN!

SO here is the solution to this..

1. IF YOU ARE USING DEFAULT JOOMLA REGISTRATION PROCEDURE;

Goto /components/com_registration/registration.php:
replace 'Registered' with 'Author'

function saveRegistration() {
global $database, $acl;
...
$row->id = 0;
$row->usertype = '';
$row->gid = $acl->get_id( 'Author', 'ARO' );
...

2. IF YOU ARE USING COMMUNITY BUILDER;

Goto /components/com_comprofiler/registration.php:
replace 'Registered' with 'Author'

function saveRegistration() {
global $database, $acl;
...
$row->id = 0;
$row->usertype = '';
$row->gid = $acl->get_id( 'Author', 'ARO' );
...