Observers are the particular classes that control the general behavior, performance, or change in the business logic of the store. They are executed whenever a specific event for which they were set to listen is triggered.
To create an observer in Magento 2, you must place your class file under the
ModuleRoot/Observer directory. The observer class file should use
Magento\Framework\Event\ObserverInterface class and define the executive function.
Events are dispatched by Magento 2 modules whenever specific actions are triggered. When an event dispatches, it passes data to the observer that is configured to watch (or monitor) that event. You can dispatch Magento 2 Events using the
Magento\Framework\Event\Manager class. This class can be obtained through dependency injection by defining the dependency in the constructor method of the class.
To dispatch an event, you have to call the dispatch function of the event manager class, providing the name of the event along with an array of data that you wish to deliver to observers.