Lets start the Drupal 8 learning with making a simple form and how to create a simple custom module. This custom module would be called as hello_world.

  • STEP 1: I am going to make "hello_world" folder which can be placed inside custom under modules in the sites root folder. Create a file hello_world.info.yml (Drupal 8 has introduced yml format, we should be very careful about spacing here).
    Below shows the code that I have put in the info.yml. 
    name: Hello World
type: module
description: test module by nitish
core: 8.x
package: nitish
dependencies:
    -drupal:views
configuration: hello_world.settings
php: 5.6
    After this the module should start coming up in the module list under the extend section in the site.

  • STEP 2: Now we will create a route(A route is a path which is defined for Drupal to return some sort of content on. For example, the default front page, '/node' is a route. When Drupal receives a request, it tries to match the requested path to a route it knows about. If the route is found, then the route's definition is used to return content.) In drupal 7 we used hook_menu but this has been removed from drupal 8. We are using routes here now.
    To start make a file hello_world.routing.yml file in the hello_world module folder. 
    hello_world:
    path: 'hello_world'
    defaults:
        _title: Nitish is best.
        _controller: '\Drupal\hello_world\HelloWorldController::content'
    requirements:
      _permission: 'access content'
    Here we defined the path which is set to hello_world. The title of the page is Nitish is best.
    Controller is set to HelloWorldController files content function(HelloWorldController::content).
    Permissions is also set to 'access content'.
  • STEP 3:
    • Our Controller file.
    Now our controller file `HelloWorldController.php` file would be placed in our hello_world module inside src folder in Controller folder.
    So the path would be hello_world->sr->Controller->HelloWorldController.php
    It would contain 
    /**
 * @file
 * Contains \Drupal\hello\HelloController.
 */

namespace Drupal\Controller\hello_world;


use Drupal\Core\Controller\ControllerBase;


class HelloWorldController extends ControllerBase {
  public function content() {
    return array(
        '#markup' => '' . t('Hello there!') . '',
    );
  }
}


    Here you can see new stuff like namespace, class, extend.
    namespace: came from PHP 5.3 why it is needed: As we use different libraries, modules, we can accidentally resuse a function or class name that has been declared before. namespaces: can be seen as a particular space provided to our module where we can declare variables and classes.
    Class: Comes from object oriented programming style. It is wrapper which contains the logic of defination of same kind of methods and variables which would be used.
    Objects: Instance of class. An object is a specific instance of a class; it contains real values instead of variables.