Hướng dẫn abstract class constructor php

I followed this link already before asking - Answer is in JAVA context and this for constructor in PHP .

Since I am starter, my implementation of my PHP code in OOP concepts, so I am really willing to know about the usage and benefits or when to use constructor in PHP abstract class.

Please provide an example in real world context to grab the concept better.

PS - Although I am following PHP Manuals to understand OOP concepts but I am finding it little bit hard to understand, any help with the links/blog to follow is really appreciable.

My Code -

The above example will output:
ConcreteClass1
FOO_ConcreteClass1
ConcreteClass2
FOO_ConcreteClass2
Example #2 Abstract class example