Magento community provides us with a great variety of modules (free and paid), available for downloading and installing from Magento Connect catalog, and from 3rd party developers' websites. Together with the rich Magento functionality, this allows us to solve a lot of tasks without programming skills. But, what if there is no solution for your specific task? Or, what if the needed module doesn't quite work as you need. Unerstanding of Magento architecture will help you to make changes to the existing modules or create your own module from scratch.
For more about magneto module development information:https://mementia.com/creating-custom-magento-module