So how does theoretical physics "work" exactly?

To explain, I'm just a big old ignorant layman, but with other scientific fields I at least CONCEPTUALLY understand how they came to their findings.

Like if a Geologist tells me something about rocks I'm like: "Okay, idk how geology works, but I assume you did some kind of experiments involving rocks so you probably know what you're talking about."

Or if a neurologist tells me something about the human brain: "Okay, idk shit about neurology, but I assume you did some kind of brain scan or took some brain samples or did some kind of scientific experiment thingy to know this stuff about brains. I don't know the exact details but I can at least abstractly understand the process by which you learned this thing you're telling me now."

Then I'll see some news report about some finding a theoretical physicists made and it'll be like: "The Universe is made of strings! And also the sun is a black hole! The universe is shaped like a doughnut!"

And my honky ass is just like: "How the fuck do you know that shit? What are you looking at? How did you figure that crap out?"