Multi Site is one of the best features in WordPress.
wp-config.php
Add the following line in your wp-config.php file (in your root folder).
define('WP_ALLOW_MULTISITE', true);
Network
A new menu item will show up under the Tools section 😉
More info - http://codex.wordpress.org/Create_A_Network
Sub directory method
Sometimes it might install the sub-domain method by default.
If that happens use this wp-config lines:
# BEGIN WordPress
RewriteEngine On
RewriteBase /
RewriteRule ^index.php$ - [L]
# uploaded files
RewriteRule ^files/(.+) wp-includes/ms-files.php?file=$1 [L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule . index.php [L]
# END WordPress
Make sure you use this .htaccess rules:
# BEGIN WordPress
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [L]
# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^[_0-9a-zA-Z-]+/(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^[_0-9a-zA-Z-]+/(.*\.php)$ $1 [L]
RewriteRule . index.php [L]
# END WordPress