Dependency Injection Understanding

Lets read the following post for understanding Dependency Injection in real life:
http://www.theserverside.com/news/1321158/A-beginners-guide-to-Dependency-Injection

Dependency Injection in PHP:
http://krasimirtsonev.com/blog/article/Dependency-Injection-in-PHP-example-how-to-DI-create-your-own-dependency-injection-container