Magento is an open-source content management system for e-commerce website. Magento employs employs the MySQL//MariaDB relational database management system, the PHP programming language, and elements of the Zend Framework. Unlike other platforms such as Wordpress, Joomla,... Magento is designed to be highly compatible with functions of an ecommerce website.
What is Magento Extensions?
Platform is just the beginning of an ecommerce website. Magento allows you to build ecommerce website from scratch with basic functions such as checkout, display shopping cart, payment,... However, Magento doesn't provide enough functions or sometime the processes are too complicated. Merchants need Magento extensions so that they can optimize online stores.
For example, you're planning to reward customers on their behaviors but Magento doesn't offer that kind of function. That is when you need Magento Extension. The screenshots below are example taking from Reward Point Plus Extension of Magestore.
As you can see, this is front-end after installing Reward Point Plus. Customers can track the reward points and the balance of points.
As for back-end, this is the demo.