Noob Q: Headers in C++

They are basically files that are copied into the .cpp file where the #include directive is present. They normally contain type, function, class definitions. The compiler needs these definitions if you are to use these functions eg. cin, cout, printf, MessageBox, etc. Or types DWORD, BYTE, ULONG, size_t, etc.

By including a type, classes header in another file you can use that type or class in that file. That's how the become a map between .cpp files.