How to expose a function in a DLL writen by C#?

[heack]

in C++ we could use "__declspec(dllexport)" keyword to expose a function, but How could I make A function in a class exposed to VBA(excel).
In order to call a function in a C++ DLL, I could use declare sentence, but How could I declare a reference to a C# DLL? It always throws errors: cannot find entry point xxx(function name). Could Anyone give me the keyword to expose the function in C# DLL and I will greatly appreciate !

[Curtis Rutland]

Look up DllImport
that would be dll import (the l and the capital i look the same).

[Plater]

If you want to use your managed DLL as a COM object, you need to set the ComVisible property and I think register your DLL