I'd recommend the book 'A Brief History of Time' by Stephen Hawking, or for the math side, 'The Joy of x.' Your library has them. They're written for curious regular people. You don't need a degree to understand the big ideas.

I teach high school science and I get this question every year. The textbook explanation is a simplification — a useful one, but a simplification. The real answer involves stuff you'd cover in a college course, but I can give you the gist.

Be careful about 'common sense' here — a lot of science is counterintuitive. The whole point of doing experiments is that the universe often doesn't work the way our gut tells us it should. The Earth feels flat and stationary, after all.

The math looks scary but it's mostly just a precise way of saying something you can understand in plain English. Once you get the concept, the equations are just bookkeeping. Focus on the idea first, the symbols second.