Recently about 5-10% of our Joomla questions on the forum have in some manner been related to the infamous htaccess file. This tutorial will give you a sample of what a typical Joomla htaccess should look like in case yours is blank or badly misconfigured. Please understand that not all htaccess files will look like this, although this is the norm for most cases.
Please note that any line that begins with # is commented out and therefore will not be executed by the server.
Typical Joomla htaccess file
# @version $Id: htaccess.txt 10492 2008-07-02 06:38:28Z ircmaxell $
# @package Joomla
# @copyright Copyright (C) 2005 - 2008 Open Source Matters. All rights reserved.
# @license https://www.gnu.org/copyleft/gpl.html GNU/GPL
# Joomla! is Free Software
##
#####################################################
# READ THIS COMPLETELY IF YOU CHOOSE TO USE THIS FILE
#
# The line just below this section: 'Options +FollowSymLinks' may cause problems
# with some server configurations. It is required for use of mod_rewrite, but may already
# be set by your server administrator in a way that disallows changing it in
# your .htaccess file. If using it causes your server to error out, comment it out (add # to
# beginning of line), reload your site in your browser and test your sef url's. If they work,
# it has been set by your server administrator and you do not need it set here.
#
#####################################################
## Can be commented out if causes errors, see notes above.
Options +FollowSymLinks
#
# mod_rewrite in use
RewriteEngine On
########## Begin - Rewrite rules to block out some common exploits
## If you experience problems on your site block out the operations listed below
## This attempts to block the most common type of exploit `attempts` to Joomla!
#
# Block out any script trying to set a mosConfig value through the URL
RewriteCond %{QUERY_STRING} mosConfig_[a-zA-Z_]{1,21}(=|\%3D) [OR]
# Block out any script trying to base64_encode crap to send via URL
RewriteCond %{QUERY_STRING} base64_encode.*\(.*\) [OR]
# Block out any script that includes a tag in URL
RewriteCond %{QUERY_STRING} (\|%3E) [NC,OR]
# Block out any script trying to set a PHP GLOBALS variable via URL
RewriteCond %{QUERY_STRING} GLOBALS(=|\[|\%[0-9A-Z]{0,2}) [OR]
# Block out any script trying to modify a _REQUEST variable via URL
RewriteCond %{QUERY_STRING} _REQUEST(=|\[|\%[0-9A-Z]{0,2})
# Send all blocked request to homepage with 403 Forbidden error!
RewriteRule ^(.*)$ index.php [F,L]
#
########## End - Rewrite rules to block out some common exploits
# Uncomment following line if your webserver's URL
# is not directly related to physical file paths.
# Update Your Joomla! Directory (just / for root)
# RewriteBase /
########## Begin - Joomla! core SEF Section
#
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !^/index.php
RewriteCond %{REQUEST_URI} (/|\.php|\.html|\.htm|\.feed|\.pdf|\.raw|/[^.]*)$ [NC]
RewriteRule (.*) index.php
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{https:Authorization},L]
#
########## End - Joomla! core SEF Section
Configuring the htaccess File for SEF URLs in Joomla
Please visit this tutorial: The Ultimate Joomla SEF URL Guide