Event and Observers in Magento2

To create observer in magento2, first we need to define observer in file:

app/code/Rahul/HelloWorld/etc/events.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="controller_action_catalog_product_save_entity_after">
        <observer name="Rahul_HelloWorld_Product_Save_After" instance="Rahul\HelloWorld\Observer\ProductSaveAfter" />
    </event>
</config>

Note: There are different places to create files for different handlers.

    To create observer for frontend you can create file under : app/code/Rahul/HelloWorld/etc/frontend/event.xml
    To create observer for frontend you can create file under : app/code/Rahul/HelloWorld/etc/adminhtml/event.xml
    To create observer for both end, you need to create file under : app/code/Rahul/HelloWorld/etc/event.xml

After this file, you need to create your observer file at the path you have mentioned above, i.e.:

app/code/Rahul/HelloWorld/Observer/ProductSaveAfter.php
   
<?php
namespace Rahul\HelloWorld\Observer;

use Magento\Framework\Event\ObserverInterface;

class ProductSaveAfter implements ObserverInterface
{
    protected $_objectManager;
   
    public function __construct(
        \Magento\Framework\ObjectManagerInterface $objectManager
    ) {
        $this->_objectManager = $objectManager;
    }

    public function execute(\Magento\Framework\Event\Observer $observer)
    {
        $storeId = $observer->getEvent()->getData('store_id');
        //Do your stuff here!
        die('Observer Is called!');
    }
}