Some of the first things we must consider when starting a philosophical analysis of something is what are the necessary conditions and what are the sufficient conditions for the idea being considered? In this case, what is necessary for one to have or do to know something? And, what is sufficient for one to have or do to know something? The traditional answer to this question goes back to Plato's time (though I haven't personally studied Plato's epistemology), that is, a true, justified belief. Belief, in this sense isn't the same as a religious or political belief (per se), rather a stab at the truth in thought. One cannot think something is false and yet believe in it. So, belief in its nature includes at least the attempt at truth, though one can guess at something and end up getting it wrong. Justification is important for knowledge because, if one is to be rational, one cannot just say, "I believe this or that just because" or if one refuses to consider objections to one's beliefs they're being irrational. Also, without justification things can end up being true by guessing and that's not complete knowledge either. These things seem to be necessary conditions for knowledge, but as we'll see with the examples they aren't necessarily all the sufficient conditions for knowledge. Let's move on to those examples because, to me, they're the fun parts of this concept.
Example number one to show how having simply true, justified beliefs are not enough to claim knowledge. Suppose my brother comes to visit me every Tuesday afternoon, and it's a Tuesday and I'm expecting him and my friend, who is generally trustworthy, tells me my brother is at the door. However, for whatever reason, my friend happens to be lying this time (the reason for the lie is not important), and my brother is not at the door. At first we have an untrue, but justified belief that my brother is at the door. However, as I'm going to meet my brother at the door, unbeknownst to my friend, my brother shows up at the door. Did I know my brother was at the door? No, not really even though it was true that he was at the door and I was justified in that belief. But, no I didn't know that he was at the door at any time. The second one is better (at least I think so). You're driving through the countryside and you're seeing all the typical things one would expect to see, fields with bales of hay or straw, barns, livestock, etc. Then, without realizing it, you are driving along and the things you've been observing, are now all fake. So here we have justified beliefs (that the things we're seeing are real) but they're not. Then, without your knowledge of it being so, there's a real barn in amidst the fake. There, you have a true (at least about that one real barn) justified belief. But that doesn't seem to be enough for knowledge in this case.
So there you have it, true, justified beliefs are required to have knowledge of something, but apparently are not the only things necessary to know something. There have been many arguments and there doesn't seem to be any clear answer to what else needs to be added to true, justified beliefs to comprise true knowledge. I certainly don't have the answers, again I'm just bringing up the question. According to Prof McGinn's lecture it seems that there has to be some kind of causal relationship the truth and the belief(s) to be true knowledge.
Here's my only divergence from Prof McGinn. I'm not saying that it's true knowledge, but I would posit that having a justified belief can lead to one believing that something is true to the point that it's true to that person. Take the characterization of the mathematician, John Nash, in the movie A Beautiful Mind, the character played by Russel Crowe is plagued with delusions so powerful that he truly believes that they're real. So, in effect, they become real to him. It may not make any difference in reality, but to the individual things that are not true, with enough justification and powerful enough belief it can become real to that person.
What does this mean to you and me? Honestly, not much. I believe that there's a personal creator God. There are many different justifications for that belief, they're generally covered in apologetics. No one can prove or disprove the truth of that claim, but at least two of the necessary conditions for knowledge have been met for me.