Lets see How to enable Mod-Rewrite Module and The first line of this text file should be:
RewriteEngine On
After that you can place your rewrite rules. Here are some examples for Joomla’s SEF option:
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} (/|.htm|.php|.html|/[^.]*)$ [NC]
RewriteRule ^(content/|component/) index.php