Magento 2 – Event for Success Page

I'd recommend adding a block via XML with its own template. It'll make it a little cleaner since it won't fill up the success.phtml file.

Step 1:

In your app/design/frontend/YOUR_PACKAGE/YOUR_THEME/layout/local.xml (This file is optional, so if you don't have one, create one)

<?xml version="1.0" encoding="UTF-8"?>
<layout>
    <!-- success page view -->
    <checkout_onepage_success>
        <!-- references the main body of the page -->
        <reference name="content">
            <block type="checkout/onepage_success" name="whatever.you.want" as="order_items" template="checkout/success/items.phtml" />
        </reference>
    </checkout_onepage_success>
</layout>

Step 2:

In your app/design/frontend/YOUR_PACKAGE/YOUR_THEME/template/checkout/success.phtml file, add the following call to request the block we just created. You can place it anywhere you'd like it to show up.

<?php echo $this->getChildHtml('order_items') ?>

The order_items references the as="order_items" attribute in my example local.xml file, so you can change it to whatever you'd like. Just make sure to change both of them.

Step 3:

As you can see, we're referencing a phtml that doesn't exist in the template="checkout/success/items.phtml" attribute. You need to create this file at that location. (You can change this location to whatever you'd like) So for this example, it should be at app/design/frontend/YOUR_PACKAGE/YOUR_THEME/template/checkout/success/items.phtml

In this file we can get the items and various data from the items with something like:

<?php
/*
 * joaogdesigner
 * custom items for the success page
 *
 * @category design
 * @package your_package
 * @block Mage_Checkout_Onepage_Success
 *
*/
    $order = Mage::getModel('sales/order')->loadByIncrementId($this->getOrderId());
    $items = $order->getAllVisibleItems();
    $total = $order->getGrandTotal(); // grand total
?>

<?php foreach( $items as $item ): ?>

    Product ID: <?php echo $item->getProductId(); ?>
    Name: <?php echo $item->getName(); ?>
    Qty: <?php echo $item->getQtyOrdered(); ?>
    Price: <?php echo $item->getPrice(); ?>

<?php endforeach; ?>

Hope this helps! Let me know if you need anything clarified.

Assuming you have created custom module to do this operation .

So in your Vendor_Module directory create one directory called etc.

In etc directory create one file called events.xml

Put below code in events.xml file

<?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="adminhtml_customer_save_after">
        <observer name="Vendor_Module_Customer_Save_After" instance="Vendor\Module\Observer\Customersaveafter" />
    </event>
</config>

Now you need to create observer for the same . so create directory called Observer in your Vendor/Module Directory

In your observer directory create Customersaveafter.php file

<?php
/**
* Copyright � 2016 Magento. All rights reserved.
* See COPYING.txt for license details.
*/

namespace Vendor\Module\Observer;

use Magento\Framework\Event\Observer as EventObserver;
use Magento\Framework\Event\ObserverInterface;


class Customersaveafter implements ObserverInterface
{
    protected $_request;
    protected $_layout;
    protected $_objectManager = null;
    protected $_customerGroup;

    /**
    * @param \Magento\Framework\ObjectManagerInterface $objectManager
    */
    public function __construct(
        \Magento\Framework\View\Element\Context $context,
        \Magento\Framework\ObjectManagerInterface $objectManager,
    ) {
        $this->_layout = $context->getLayout();
        $this->_request = $context->getRequest();
        $this->_objectManager = $objectManager;
    }

    /**
    * @param \Magento\Framework\Event\Observer $observer
    * @return void
    */
    public function execute(EventObserver $observer)
    {
        echo "Do your operaiton here";
    }
}

Note : adminhtml_customer_save_after event is called after adding the customer