You need a large whack of Carbs that act FAST to halt catabolism and shift you towaard anabolism. Also the carbs are used to refill your depleted glycogen. So some is used right away to refill liver and muscle glycogen, and then you still need surplus to be used as fuel to stop the catablolic state and help to begin to rebuild in an anabolic state, enter the protien aminos. Plus this PWO shake will be digested very fast and you should be then eating a whole food meal with a nice load of whole food protien shortly after.
Thats the basics.