Oh, all right.
But before I start, let me say that I like Plato for a lot of reasons. Maybe this is bordering on blasphemy for an Aristotelian, but I think Plato established the most extraordinary organization in history: the Academy. The Academy under Plato was a playground for thinkers. Under Plato, his organization tolerated opposing views--as long as they stood up to scrutiny. The Academy drew the world's greatest thinkers, some of them escaping tyranny to live in Athens. In the Academy, Eudoxus was allowed to teach what he thought was right. In the Academy, Aristotle was allowed to openly criticize Plato and others. Looking at the progression of ideas from the Republic to the Laws, the Academy was a place where even the teachers could learn from their students. (After Plato died, Speusippus dorked the whole thing up--that's my view anyway).
In Plato's philosophy, what we roughly call the real world isn't real at all, but just a shadowy copy of the world of the Forms. The particulars, the things of this world, can only be real to the extent that they "participate in the Forms." Something that's considered beautiful merely participates in the Form of Beauty to some extent. There aren't just Forms for complex concepts like beauty and justice, but for man as well.
Somewhere, according to Plato, is a perfect Man of which we are all just imperfect reflections. The world of the Forms is a supernatural realm populated with the ideal structures of particular things: universals. These two separate worlds come together in the mind of a man only to the extent that he can remember the Forms from some inter-life stage in his development. (Plato believed in an eternal transmigratory soul that moves from body to body through birth, death and rebirth--an eastern import. The ancient Greek man on the street would have laughed at this--I'll see you in Hades' Halls!). Plato's version of rationality consists of being able to "see" the participation of the universal in the particulars that "exist" in this shadowy world in which we (allegedly) live. If you're rational in the Platonic sense then you can look at a beautiful human, Achilles, and "see" that his body participates more in the Form of beauty (is closer to perfect beauty) than the body of an ugly man, Thersites, who, according to Homer, was "the ugliest man who came beneath Ilion."
Epistemology is the study of knowledge, how we know things, how knowledge gets into our heads.
Epistemology for Plato required the innate ability to "see" the supernatural world of Forms. Those few with the clearest sight of the Forms would, with extensive training, become the absolute dictators--the philosopher kings--in Plato's utopian state. A few more of the population, those with some, but not the complete ability, would hold somewhat lower positions. Everyone else is relegated to total slavery, dominated completely, treated like mindless animals, which they are according to Plato's epistemology--these people had no access to the Forms, and therefore had to be told what to do by those who did. Keep in mind that the majority, the masses, the "herd" were not born with the ability to grasp the Forms at all.
Incidentally, for Plato there's a group even lower than the herd: those damn artists. (Worthless, soul-destroying lying bastards, the lot of them). At least the mindless animals with human shapes could be directed to perform manual labor--you know, rake the leaves, take out the trash, etc.--and labor of this kind wasn't harmful to the Republic and its "citizens." Plato denounced the effect of art as "a crippling of the mind." (Rep. 595b5). Artists would be banished from Plato's utopia. (He'll keep a couple guys around to write military marches and funeral dirges. The rest of you--OUT!).