The examples/ directory contains copy-pastable example snippets. examples/cpp/ contains example C++ header files, and how to call them from Rust -- for example, examples/cpp/function shows how to call a C++ function from Rust. examples/rust contains example Rust modules, and how to call them from C++.
In every case, examples have the following files:
example.h or example.rsmain.rs or main.cc.example_generated.rs or example_generated.h. This isn't something you should ever use directly, it is only here for exposition. (The checked-in copies of what Crubit generates are kept in sync using a golden test framework, but ordinarily, you will use the C++ header / Rust module that Crubit generates on the fly, dynamically.)