Is there anywhere in the docs that discuss what a Contract ID is/how they work?

For Contract Keys I find this: https://docs.daml.com/daml/reference/contract-keys.html

But for Contract IDs I can’t find an equivalent.

https://docs.daml.com/daml/stdlib/Prelude.html#type-da-internal-lf-contractid-47171 has almost all there is to say about it. It’s just a unique identifier for a contract that you should treat opaquely. https://docs.daml.com/concepts/ledger-model/ledger-daml.html describes it on a slightly more abstract level.