Definition of Purpose: the reason for which something is done or created or for which something exists. Definition of Serve: perform duties or services The purpose of a knife is to cut things. The purpose of a glass is to hold a drink. The purpose of a car is to take you to another place. The purpose of movie is to entertain us. Other ways to ask the question: For what purpose does it serve? What service does it provide? Why was it created? What is it for? Why is it needed? I hope that helps.

It could mean: What is the point of it? What is it used for? Why do we have it? You might ask 'What purpose does it serve?' when you think something is unnecessary.