www.drupaltutorialcenter.com

Take a look at this link for a complete explanation of Clean URL's in Drupal.

Clean URL is an URL, which looks like:
http://www.yoursite.com/cleanurl
or http://www.yoursite.com/vegetables/cucumber
or http://www.yoursite.com/cucumber.html
or http://www.yoursite.com/vegetables/cucumber.html
or http://www.yoursite.com/vegetables/cucumber.php
etc.

This tutorial covers the question "What's a Drupal Node?". For an in-depth answer, please see What's a Drupal Node.

Updating Drupal is a very important issue for every Drupal maintainer or administrator, since it allows you to keep your project up to date with all bug fixes and security patches. Take a look at this in-depth tutorial on Updating Drupal, or keep reading this tutorial for a more basic explanation of the Drupal updating process.