Drupal 8 uses events to allow modules and various subsystems to communicate with one another in an object-oriented manner. Understanding how the Event API works is critical knowledge for all module developers.
Understand Drupal Events versus Hooks
Create an Event Subscriber with tags
Dispatching an Event
Discover Existing Events
Explain what events are, and their use case. Provide direction for people who want to learn more about working with events in their code.