How do I know what I know?

             This question is tripping me out quite a bit. Is the question asking how have I come to learn everything that I know today? Or is it much deeper? Is the question asking how do I know that everything I know is true and real? I'm going to answer the first interpretation first, as my brain will still be intact by the time I've finished answering.

              I think that there are two different ways to know something: having it taught to you, and discovering whatever it is on your own. The latter, however, is the only true way of knowing something. I mean everything we're taught is probably true, like for example: the american revolution. Obviously we all know it happened but for sake of the argument let's just say there was no actual proof. We were taught that it happened, but because we weren't actually there, how can we be 100% positive that it actually even occurred? The only way to truly know something is to have it happen directly to you. For example, when I was little my mom told me not to put my hand on the grill because I would burn myself. Although she told me what would happen, I didn't really learn not to touch the grill until I touched it anyways and suffered the consequences.

             As for the deeper version of this question: how do I know that everything I know is true and real, I do not know. This goes back to the cave wall, because everything that I might think to be something might be something larger or completely different in the grand scheme of things. Maybe everything I see is an illusion. The only thing I really know and am aware of is my own consciousness, therefore maybe everyone else in the world are robots or figments of my own imagination. That's some crazy stuff right there.