The Strategy Pattern is used to decouple an algorithm from the context in which it is used. I'm going to equate this example to a real world scenario starring a man, I'll call him Bob.
In his example Bob heads to work and takes whatever way he wants to get there. His boss only cares that he makes it there, not the path he takes. Bob can take many different ways ("strategies") to get there, but how is up to him. Tom illustrates this with a bit of sample code with a "bob.php" that can use any number of other classes/methods to get to work (like commute, the train or a car).