Core concepts in Drupal include blocks, hooks, forms, and menus. Understanding how these things work and interact with each other is critical when you build custom modules.
The main method used to modify the Drupal core or any contributed module is through the hook framework. This is what gives Drupal its flexibility and, frankly, makes things really hard to understand at first. Without inspection tools like tracing debuggers, it is difficult to follow who is grabbing the page, processing it at what point in the page lifecycle, and what they are doing with it.
The Drupal bootstrapping framework takes care of making sure that anyone who needs to have a say in how the page is built gets to have their say.
In order for ...