What happens to your muscles when you work out?

Specifically down to your muscle fibers. I only vaguely remember glossing over this in class years ago. I’m particularly interested in what happens to them when you work out and what it means when you’re sore, also what happens to them after you DON’T work out for a while and your muscles “shrink” back to normal.

I was under the impression that these muscle fibers snap when you work out and get sore, and your body “ties” them together again but this time makes them bigger so it doesn’t tear again. But I’m not sure if that’s an accurate visual.