If you’re looking for solution to customizing Magento admin core functionality or want to change core functionality of any controller. Don’t worry, it’s really very easy. You just need to override controller action with your controller action. In this tutorial, I have explained how to override Magento admin controllers.
magento tutorial
Magento – Create Custom Module with Custom Database Table
You can easily create Magento custom modules by going through the common modules structure of Magento. Here in this tutorial, we have explained all required module structure for creating custom Magento modules.