What is epistemology? It is the quest to understand, why we think we understand something; why we feel, we are entitled to claim we know, or understand, which latter term I prefer, because like Socrates, I believe "I know that I do not know," or rather "I understand that I do not know," or even more adequately: "I feel, I have good reasons to assume that I do not know."
"I know that I do not know" sounds pretty absurd, though. After all, we know a lot of things for sure, do we not? Two points to open the mind to the deeper meaning of Socrates insight: (1) There are definitional truths, such as used in Mathematics or Formal Logic. Here we define what is true, and such tautologies may well be exempted from Socrates' proposition, it would seem.
(2) However, powerful tools of reasoning, such as mathematics, using tautological input, are arrived at in the same way as any other model that helps us better understand the world; they are brought about by trying out conjectures, which we refute, if they produce contradictions and adhere to for as long as we have not come across circumstances that contradict the as yet unchallenged hypothesis.
The "knowing" that Socrates refers to is the overall and ongoing process of learning more about the world.
The essential point that Socrates is making suggests that we should never consider the process of corroboration completed. The best we can hope for are powerful hypotheses which in principle are always open to new intellectual or factual discoveries that prove our supposed "knowledge" (truly our hypothetical assumptions) to be false. The fact that some of these assumptions appear immensely robust should not discourage us from always adhering to Socratic humility. It is fine if certain things seem to be ultimately true, or are even ultimately true; but this should not be used as an excuse to exempt them from efforts of corroboration. Assuming this attitude in the face of the most unshakable certainties (Newton's physics) is what made Einstein the intellectual giant that we rightly have come to take him for.
In your quest for the truth, never ever take anything for granted.
Consider the context within which Socrates' dictum was coined. Once this question was put to the Delphic Oracle: "Is there any one who is wiser than Socrates?" Much to Socrates shock, the Oracle replied: "No, there is no one who is wiser than Socrates." Flabbergasted at the statement, for Socrates knew just how lacking in wisdom and knowledge he was, he decided to corroborate the flattering hypotheses. Thus, he looked up men that claimed of themselves or were regarded as being wise: statesmen, judges, artisans. On talking to them, he discovered that they were not wiser than he was in his negligible wisdom and knowledge; however, these men thought they were wise and knowledgeable. And in this respect, he realised, they were in fact less wise and knowledgeable than he himself.
And so, Socrates came to interpret the meaning of the Oracle's statement in this way: The Oracle did not actually have Socrates in mind, when making its pronouncement, it was rather making this point: It is he amongst human beings to be considered the wisest, who recognises, like Socrates, that he is lacking in wisdom."
The most powerful tool of the human mind is intellectual humility of this kind, from which emerges a critical and open attitude.
This insight has important implications for politics, as a comparison of Plato and Socrates shows. Both thinkers demanded that statesmen should be wise. However, to Socrates this desideratum implied that statesmen should be aware of how little they know, while Plato felt that those with the best possible education thereby acquired the right to exercise "sophocracy," the rule of the wisest men that the rest of the population ought to be subjected to.
Socrates emphasised the conjectural nature of "knowledge" and rejected, therefore the idea that "knowledge" or the bearers of "knowledge" possessed exceptional authority. Approaching truth to the extent men is capable of is a humble process of critical exchange, where every contribution counts and authority lies with the process of critical debate and corroboration but not with the "gurus".
Socrates epistemology is intimately intertwined with the love of liberty and the superior power of freely interacting, decentralised knowledge.
Socrates would have loved the American Constitution, after all, he observed the principle "live free or die," and paid with his life for it. Socrates insisted on the rule of law, refusing to submit to the "rule of man." But that is a story for another post.