title: Overriding Magento Admin Controller, for Beginners
body: <p>In the Magento Admin section, I want to override the "Sales/Order/ShipmentController.php" controller file of the core Mage.</p>
  
  <p>I have tried rewriting the URL, using the "from" &amp; "to" tags, but in vain.<br>
  I don't know what is the actual &amp; correct way of doing this, as I'm a newbie in Magento.</p>
  
  <p>Please anybody provide some good fundamental &amp; correct answer, so that at least the concept gets clear.</p>
  
  <p>Also, if possible, please tell me, what is the actual purpose of the controller, for both the frontend &amp; the back-end?</p>
  
  <p>Any help is greatly appreciated.</p>