In Plato’s allegory of the cave, he portrays the common man as a prisoner, chained so that he can only see the shadows of real things, not reality itself. However, the philosopher can escape from of the cave and see the real world as it is.
What Plato is driving at here is that there is much more to reality than what we can see with our eyes. Plato believed that all the physical things in the universe have absolute archetypes, called forms, that exists in a separate universe. This separate universe is not physical, nor does it exist only in the minds of human beings. What we can see are simply physical examples of the forms.