basically, the entire TL;DR of this post, from someone who is a linux nerd, that knows some things about networking.

Everything knows where everything is, and if it doesn’t it knows something else that does, and if that doesnt, well, repeat adnauseam. The technicality here is that not every individual point knows where every other individual point is, but it knows it’s immediate neighbors. And those immediate neighbors do as well, at the high routing level, think data center.

Think of it like a tree structure, but a really fucking big one, and with a lot of circular and unusual connection points. You can get from one point, to any other point. It’s just a matter of knowing how.

Also, to be pedantically accurate here, the internet is a hodge podge of packet flinging hardware, “routes” aren’t really a thing. Packets will take whatever route is determined to be optimal by the hardware it interacts with. I.E. it dynamically changes as needed, that’s why your ping is always variable