How do you go about using mod_rewrite, Ive heard by using this, your site becomes SEO friendly?

mod_rewrite is a mod in Apache. To use it first you should have Apache running as your web server and mod_rewrite should be enabled.

What it does is, it just rewrites a url in a different way.
How it makes the SEO friendly, well, if you are aware that when you use ? in the url, its not that use friendly (Please note that Google now does crawl these pages, before it dint). These pages are often given lower PR as they are considered part of the same page.

For eg:
take this current thread url
http://www.uniquewebmaster.com/showthread.php?tid=136
So, the url http://www.uniquewebmaster.com/showthread.php gets higher PR than but, http://www.uniquewebmaster.com/showthread.php?tid=136 gets lower even though its totally different url in users opinion.


Now , you can type in this url in the browser
http://www.uniquewebmaster.com/showthread.php/tid/136
This looks a totally different url.
With mod_rewrite (in .htaccess) you can rewrite this url to the original one. The url that the script will receive will be
http://www.uniquewebmaster.com/showthread.php?tid=136

But for users and SEs, it'll still be
http://www.uniquewebmaster.com/showthread.php/tid/136

Hope this helps

jaswinder pretty much explained it - you should post the question in the apache section (is there an apache section?).