$ An Observer, also called 'listener', will listen to your program to detect events. When there is an event taking place, it will perform an action defined by you.
File path: app/code/local/MageCheck/Tutorial/etc/config.xml
File path: app/code/MageCheck/Tutorial/etc/events.xml
File path: app/code/local/MageCheck/Tutorial/Model/Observer.php
File path: app/code/MageCheck/Tutorial/Controller/Index/Test.php