Here's a detailed mod_rewrite explanation I posted a while ago for another user, hopefully it helps you!
Well it does both. See what happens is this:
The Server (aka Apache) doesn't understand http://mydomain.com/page/about-us/27. To that it will understand it as folders and sub-directories.
So, in order for Apache to understand it, the mod_rewrite transforms that into the long string listed above according to your re-write rules.
So essentially what you're doing is all the links the user sees are the nice, clean ones. The only time the long index.php?p=about...etc. links appear are internally to apache - never seen by the user.
To achieve this, you use mod_rewrite. For example lets say I've got this architecture:
http://mydomain.com/index.php?p=my-page&articleNumber=38
I don't want the user to see that mess, so I use mod_rewrite.
I want users to type it in this format: http://mydomain.com/page/<page-name>/<article-number>. So lets tell apache that's what we want:
RewriteEngine On
RewriteBase /
RewriteRule ^page/(.*)/(.*)$ index.php?p=$1&articleNumber=$2
Definitions:
(.*) - This is REGEX (http://www.zytrax.com/tech/web/regex.htm) essentially meaning that it accepts any character into that spot within the link
$ - In the inital statement this signals the end of the REGEX expression
$1... $2... $n - This signals the regex expression you are relating to. So the first instance of (.*) is $1, the second instance is $2, and so on.
That's a quick run-over of it for you. If you are interested in learning it, I highlighy recommend you check out this tutorial (http://www.easymodrewrite.com/). I used that one to start teaching myself mod_rewrite and it is very helpful.
