I'm a high school senior and feel like I don't actually understand why math works, even very fundamental things like the commutative property. For example, why does 3x2, which is 2+2+2, just "happen to" equal 2x2, which is 3+3? Same goes with astand math fundamentals and how to self-learn physics & math? little more advanced stuff, like the quadratic formula, etc.

Second question, if I'd wanna self-learn math and physics (maybe chem too, as many concepts are related to physics) from the ground up, how can I do that (what are good resources)? I was thinking about starting with Khan Academy and then continuing with MIT OCW math, or do you think textbooks or something else entirely would be better?

I'd greatly appreciate help