Magento Observers and Events

 $this->_eventManager->dispatch('custom_event', ['data' => $data]);

<?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="custom_event">
        <observer name="customObserverName" instance="Oodles\Technology\Observer\CustomObserver" />
    </event>
</config>

<?php
namespace Oodles\Technology\Observer;

use Magento\Framework\Event\ObserverInterface;

class CustomObserver implements ObserverInterface
{
  public function execute(\Magento\Framework\Event\Observer $observer)
  {
    $eventData = $observer->getData('data');
    // Write code you want to perform any action.
  }
}

<?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="checkout_onepage_controller_success_action">
        <observer name="custom_sales_order_place_after" instance="Oodles\Technology\Observer\GetSalesOrderData"/>
    </event>
</config>

<?php
namespace Oodles\Technology\Observer;

use Magento\Framework\Event\ObserverInterface;

class GetSalesOrderData implements ObserverInterface
{
  public function execute(\Magento\Framework\Event\Observer $observer)
  {
        $order = $observer->getEvent()->getOrder();
        $orderId = $order->getId();
        $incrementId = $order->getIncrementId();
    // Write code you want to perform any action.
  }
}