OpenCart is a very popular CMS recent days. I'm working With open for Last 1 and half years. I was never been a writer, this is my first attempt to write something on blog. I'm going to explain and do some example how can we modify opencart coding. OpenCart is a CMS with MVC( Model–View–Controller) format. The basic File structure. Admin part: /admin /admin/controller/ /admin/model/ /admin/language/ /admin/view/ Public part: /catalog /catalog /controller/ /catalog /model/ /catalog /language/ /catalog /view/ In /system: this part is used to the open cart system run it content all the basic engine for controller,model,database and a library of some much needed model. like cart, customer, database,session etc. there are two folder /image and /download the admin and the public both use this folder for storing and showing image and other files. There are some folders need to be writable /system/cache , ...