Magento – I need add button link to a new page in Success.phtml (checkout process), how to

write an observer to get triggered on save billing or save shipping events and save the customer.

for example:

create Yournamespace_Yourmodulename.xml in app/etc/modules/

<?xml version="1.0"?>
<config>
<modules>
    <Yournamespace_Yourmodulename>
        <active>true</active>
        <codePool>local</codePool>
    </Yournamespace_Yourmodulename>
</modules>

in app/code/local/Yournamespace/Yourmodulename/etc/config.xml

<?xml version="1.0" encoding="UTF-8"?>
<config>
<modules>
    <Yournamespace_Yourmodulename>
        <version>1.0.0</version>
    </Yournamespace_Yourmodulename>
</modules>
<global>
    <events>
        <controller_action_postdispatch_checkout_onepage_saveBilling>
            <observers>
                <auto_register_shipping>
                    <type>singleton</type>
                    <class>Yournamespace_Yourmodulename_Model_Observer</class>
                    <method>autoRegisterBilling</method>
                </auto_register_shipping>
            </observers>
        </controller_action_postdispatch_checkout_onepage_saveBilling>
    </events>
</global>
</config>

in app/code/local/Yournamespace/Yourmodulename/Model/Observer.php

<?php
class Yournamespace_Yourmodulename_Model_Observer {

    public function autoRegisterBilling($evt){
        if(!Mage::helper('customer')->isLoggedIn()){
            $data = $evt->getEvent()->getControllerAction()->getRequest()->getPost('billing', array());
            $customer = Mage::getModel("customer/customer");
            $email = $data['email'];
            $websiteId = Mage::app()->getWebsite()->getId();
            $store = Mage::app()->getStore();
            $pwd = $data['customer_password'];
            $customer->setWebsiteId(Mage::app()->getStore()->getWebsiteId())->loadByEmail($email);

            if (!$customer->getId()) {
                 //Code begins here for new customer registration
                $customer->website_id = $websiteId;
                $customer->setStore($store);
                $customer->firstname = $data['firstname'];
                $customer->lastname = $data['lastname'];
                $customer->setEmail($email);
                $customer->setPassword($pwd);
                $customer->sendNewAccountEmail('confirmed');  
                $customer->save();
                   }
           }
    }
}

note :

1. this will save a customer immediately after they click continue in billing information tab.

2. you can do this on save shipping or save payment method steps.

3. if you wanna automatically login that customer, add the following in Observer.php after

   $customer->save();
   }
   
   Mage::getSingleton('customer/session')->loginById($customer->getId()); // to login that customer.
   

Swash_nam, Goto cartcontroller (app>code>core>Mage>Checkout>controllers>CartController.php)'s function goback

$this->_redirect('checkout/cart');

Go to Admin>Configuration>Sales>Checkout>Shopping Cart>After Adding a Product Redirect to Shopping Cart and make it yes