Quantum Mechanics

I still don't understand how all of this works. It doesn't make any sense! How is there an interference pattern for the double slit with the electrons? How can it go through both, then one, then none? It's impossible.

Also when there was a device to see which slit it went through, the electrons went back to behaving like marbles. It went back to producing two bands. How is this so? How could this be just because there was something watching which slit it went through? The electron acted differently just because it was being watched? How did it know that something was watching it? There were two different results, one that was being watched and one that wasn't.

From this...
How can we know that anything we have observed in the past, especially about electrons, is right?

Because no one knows really for sure whats up with quantum mechanics, I don't think that chemistry honors students should be learning about this. After "learning" and watching about quantum mechanics, many of my classmates were confused about what we just watched or "learned" about. When someone has solved the many questions of quantum mechanics, and the idea finally makes sense, then we should be taught what its about.

At least for now, probably my classmates and definitely I am very puzzled with the concept of quantum mechanics.