To create custom modules in Drupal 8, developers need to understand the main folder structure including .info.yml and .routing.yml files as well as PSR-4 autoloading. The Drupal 8 plugin system provides guidelines for creating pluggable components like blocks, fields, and entity types. For example, a block plugin can be created to add custom blocks that are managed through the user interface.

1. What we need to know
to create custom
modules in Drupal 8
Oleksandr Ivanchenko - @alexsergivan

3. Main folders structure

4. .info.yml

5. .routing.yml

6. PSR-4 autoloading standard

7. DefaultController.php

8. Plugin system
“The D8 plugin system provides a set of guidelines and reusable code components to
allow developers to expose pluggable components within their code and (as needed)
support managing these components through the user interface.”
drupal.org
Plugin systems examples:
- Blocks
- Field types
- Field widget
- Field formatters
- Image effects
- Input filter
- CKEditor buttons
- Entity types

9. Block plugin example

10. Drupal 8 forms

11. Add js

12. Drupal 8 Console scaffolding module generator
https://github.com/hechoendrupal/DrupalAppConsole