So somebody helped me out with this. You know, they say that the moon is just reflecting the sun's light. So here you can clearly see the moon and the sun and the sky together, and nothing in between them, but yet you only see a half a moon. So why is the other half of the moon not lit up if the moon is just reflecting the sun's light and there's nothing in between them?

It's because there is something in between them if you look at it from a 3D model scale, that something is the earth, and that picture, the earth is in between, the moon and the sun, at least a portion of it, and what you're seeing is that portion covering the moon.