Drupal is the world’s most powerful, most flexible and most rapidly expanding open source content management system (CMS). The truth of the matter is that it is far more powerful than commercial options as well. Drupal can be used for building just about any kind of website you can imagine, from a simple online business card to a social networking site like Facebook. The main attraction of using CMS websites rather than flat html based websites is that a content management systems allow you to edit your pages directly on the site itself. Kind of like Facebook or Myspace except with Drupal you have full control over how the site looks and how it behaves.
Drupal has the reputation of having a high learning curve. To some degree it’s true, but all depends on what your goals are. If you just want to learn how to manage a site that someone else set up for you then the learning curve isn’t that high at all. You can be adding and deleting pages from your Drupal website in minutes. Once you get the Drupal bug though, and you start wanting to create your own Drupal themes or to write your own Drupal modules then you move into new, and often intimidating territory.
Drupal was designed by very smart people who thought things out in the beginning and therefore structured the Drupal core code base in such a way that its functionality could be easily be overridden or altered using a programming interface called the Drupal Api. Likewise, its appearance is designed to be altered through the phptemplate system. On a properly built Drupal site content, functionality and styling are handled separately. The system was created in such a way to insure that it would be flexible, extensible, and easily updated. The downside to this flexibility is that it takes a little more know how to program or design within these structures.
If you are completely new to Drupal there are scores of tutorials online to walk you through it. A good technique to find the answers you are looking for is to formulate your question for in a google search and then add the word Drupal after it. There are also several good Drupal books as well which can make the process much easier.
If you are looking to build your website soon, and you haven’t made up your mind as to which system to use then I recommend you take some time to research and compare Drupal to the other options available (Joomla / WordPress). That’s how I ended up with Drupal, and in my opinion if you really do your research it’s the natural conclusion you’ll come to as well.