The Devel module provides functions and tools that aid both module and theme developers. While it is entirely fine to develop sites without it or related modules such as Theme developer, they are highly recommended as they save time and effort and will eventually prove indispensable. This recipe will outline the setup process and relevant features of the Devel module.
The Devel module can be downloaded from http://drupal.org/project/devel. Once downloaded, install and enable it via the module administration page.
From a themer's point of view, there are two primary features of importance that are provided by the Devel module. The first is the development block that can be enabled from the block administration page at admin/structure/block
[Home | Administration | Structure | Blocks]:
In the pictured development block, the most frequently used option is usually Empty cache. Clicking this link will empty Drupal's caches as...