Plato's "Allegory of the Cave," like many of his other works, is written as a dialogue between his teacher Socrates and a student. In this allegory, a student named Glaucon typically responds to Socrates' questions and descriptions with comments such as "very true" and "no question." The overall purpose of the allegory is to describe the limitations on human understanding, and to make the point that knowing those limitations leads to true knowledge.
In Plato's allegorical cave, prisoners sit chained to a wall, unable to see anything except what is directly in front of them. A fire burns between them and a row of people, who carry various objects. Because they have no other context, the prisoners believe the shadows to be reality and give names to the objects they see. If one of the shadows was a book, for instance, the prisoners would call the shadow "book" rather than a shadow of a book. If prisoners could turn their heads, they would see that the actual "book" is the object casting the shadow rather than the shadow itself.
Plato explains to Glaucon that a prisoner who turns to see the goings-on behind him will at first be uncomfortable with the sight. Just as bright light hurts our eyes when we are accustomed to darkness, reality will cause pain when we first experience it. A released prisoner may be reluctant to accept that truth, and must allow time to adjust to his new view and accept the truth he sees This revelation will inspire him to share his understanding with others.
Plato's point is that the leaders in an ideal world must be philosopher-kings, men who possess the understanding of the real world and wish to teach others. We name objects we experience through our senses and concepts we extrapolate from those experiences. Those who do possess such understanding have an obligation to help others see it. Such knowledge is important since "wisdom [is one of] the true blessings of life."