That would be like explaining C++ Concepts to an assembly programmer from the 60s that had never used a "function" as a way of abstracting code.
If you really want to know, spend one afternoon learning any programming language with built in support for that (Rust, Ocaml, Haskell, ...). ADTs is one of the first things one learns.
In Rust, the features you'd need to learn are enums, patterns, and pattern matching.
But be warned that using C++ variant and std::visit will feel like you are being forced to only write C instead of C++ for the rest of your life, knowing that life could be much better. Once you learn this, there is no way to un-learn it.
