An installation profile is a special installer that includes prepackaged modules and themes, and can configure Drupal for a specific purpose. For example, it can install and configure custom modules and themes and even set system preferences—all from the installer. So the first time you log in after installation your environment is ready.
Building an installation profile is done on two levels:
The file system: Starting from the base Drupal system, we will have to move some files around to get things configured for installation.
The .profile script: Just putting the files in the right place isn't enough. We will need to build a special
.profilescript that will perform installation tasks.
We will perform both of these. In truth, though, the file system work is simple. Most of our time will be spent generating a .profile.