Core Drupal is pretty powerful. Out of the box you have blogs, forums, pages, and books. You can highly extend the functionality of the software by adding modules to the mix. There are two ways to acquire modules. The first is to use contributed modules. Contributed modules are developed by members of the Drupal community and the contributed back for others to use. The second way is to develop a module yourself. This tutorial will focus on installing a contributed module in Drupal 5.x.

You can peruse the contributed module pool at Drupal.org and click on the Modules link.

Once you have chosen a module that fit your needs there are several steps to adding it to your Drupal instance.

1. Download the module you are going to install
2. Go into /sites/all/ and create a directory called modules
3. Extract your modules files
4. Place the files as they are extracted into the modules directory you created
5. In your Web browser, you need to enable the module. Go to /admin/build/modules and look for your module. It should be unchecked. Check the box of the module.
6. Next you need to add access to the module to what ever role you are using to administer your site. Go to /admin/user/roles and choose the role in question. Check off the module's box(es) here too.
7. Finally you need to configure and manage the new module. You can access "administer by module" at /admin/by-module.

It is a good idea to read any documentation that may exist for the module to get a better sense of what it can do and how to best configure it. Often modules include text files when you extract them. You can also read documentation on Drupal.org itself from the page that you downloaded the module itself, although the quality of documentation varies greatly.