Being an open source system for content management Drupal is based on numerous modules each of which has its own function. Some modules are built into the core of the system basic version, the others are available on the Web or can be developed specifically.
A module is considered to be a collection of additional functions that add to system functionality, so it is a very important part of the development procedure. Of course, it is possible to use ready-made modules though they do not guarantee that functionality you need. Another variant is to create a module that will meet your requirements, but it can work only if you have a good command of the menu system, APIs, know how to use different Features, implement hooks or write Drush commands. It is also necessary to be aware of coding and have configuration experience, so this task can be done only by a professional developer.