>  what didn't they explain in high school that allows this to be possible?

A ***lot*** of what electricity truly is is not covered in high school, because at that time you have neither the physics nor the math foundations to discuss the concepts.

For example, waveguide is coaxial cable with no center conductor. Heavyside had to invent vector calculus to describe coaxial cable, which he invented, and to "adjust" Maxwell's equations to the form we know today.

As a concept, shielded cable is relatively straightforward.  Far less so is how two conductors separated by a Teflon insulator can have a "characteristic impedance", just one of the consequences of the finite speed of light on how an electromagnetic field pulse propagates.

Transforms, tensors, complex vectors - there's a lot to learn and discover. Enjoy the ride.