Drupa Program Flow

Hi Frens.
I am new to Drupal. Being a php prgrammer, it will be good to know the program flow like how drupal functions flow is ,how they process and work etc.
I was wondering if there is a graphical representation of Drupal program flow.
Is it possible the program flow from somewhere. A graphical or arrow diagram sort like thing will be very helpful to all learners like me.
Thanking you all