Let us now consider the functions of each of these three parts.
Actually, we already know the function of one of the parts -- the word plays functions as the Head of this VP. The term "Head" is a functional label, indicated by the capital (upper case) letter. Remember that we also capitalize the other functions -- Subject, Object, Predicate, etc.
Turning now to the post-Head string the piano, we can see that it completes the meaning of the Head plays. In functional terms, we refer to this string as the COMPLEMENT of the Head. Here are some more examples of Complements in verb phrases: