URL rewriting are major needs for your sites that produce a dynamic pages like PHP pages with redirection pages inside your index page.

What is APACHE URL Mod Rewrite ?

URL Mod Rewrite is a Apache web server module that can manipulate your URL on fly when a visitors join your URL pages.

A mod rewrite mode is usefull to changes your original URL to all types of the URL you dreamed about.

In this link below you will find some solutions guides to use the mod rewrite scripts :

A Users Guide to URL Rewriting with the Apache Webserver
http://www.engelschall.com/pw/apache/rewriteguide/#ToC1

Why do you need URL mod_rewriting?

#1 URL manipulating

If you want to hide your original URL and what scripts that you used on it. You can use mod rewrite.

#2 Can be usefull for a Content Management System Based on Text. Content Management System has been used by 80% webmasters in the World. Ussualy they used mod rewrite to move the document root to the top level priority.

For an example :

if yout want to changes your URL from :
www.yourdomain.com/e/www

And then by using mod rewrite to change the URL to this :
www.yourdomain.com/

This module was usefull to make your web URLs look more profesional.

#3 Search Engine Optimization.

Search Engine will crawl your site with their bot scripts. By the research shows that most Search Engines were prefer a HTML pages rather than a Dynamic pages.

So that they can increase your link popularity and make they easy to crawl through your site content.

By using mod_rewrite URL manipulation , you can changes your dynamic pages to a html URL address.

For an example :
www.yourdomain.com/index.php?screen=home
You can changes it to this by mod_rewrite:
www.yourdomain.com/index.html

In other words: With mod_rewrite you either shoot yourself in the foot the first time and never use it again or love it for the rest of your life because of its power.

This paper tries to give you a few initial success events to avoid the first case by presenting already invented solutions to you.