The human brain.

I just don't get it.
Which is kinda ironic, seeing as I have to use my brain to understand my brain... but whatever. Don't want it to start hurting.
Anyway.
I mean, think about it. (No pun intended.)
How is it possible for so much stuff to be crammed in there? And why do we forget so many things?
And just WHAT is up with conjuring up images in your brain?! I still can't get how I can see an image in my head, when CLEARLY you SEE images with your EYES.
No, I never learned anatomy in high school, aside from the reproductive and digestive systems. Let's just say they felt it necessary to teach us about that kinda stuff there...