Build Custom Drupal modules using Drupal API.
A Custom Drupal module is a collection of code which is created by the user for specific needs. You should follow Drupal coding standards and write secure code.
All Drupal module must use Drupal API to build custom modules. One should not write core PHP code or any other way of coding.
With this topic, you would be able to build your own custom modules by follow Drupal's best practices.
You will also learn how write secure code that comply with Drupal coding standards.