In the previous chapter we learned how to create content, the mainstay of the Drupal website. Creating content can be accomplished using a simple build-in process. Drupal is fully usable out-of-the-box as a content management without the requirement of any customization. However, your site or business model can call for additional functionality. Perhaps you want to schedule events, or accept payments, or display a product catalog. For this reason, there is a galaxy of add-on features available that can be greatly increase its utility and flexibility.
Perhaps you have added functionality to your browser by way of a browser plugin, or to your smartphone by way of an app. With Drupal, feature expansion is also accomplished by pieces of add-on code, called modules. A module is arranged in a folder that contains program code and other files that, when placed in the correct location within the Drupal folder, provide a feature or service above and beyond...