What does #include actually do?

Question

In C (or a language based on C), one can happily use this statement:

#include \"hello.h\";

And voila, every function and variable in

Answer 1

That (copy/paste) is exactly what #include "header.h" does.

Note that it will be different for #include or when the compiler can't find the file "header.h" and it tries to #include instead.