>How can I build a DLL with Visual C++ 6.0 ?
>
>Where do I declare my functions when I use the Dynamic Linked Library Project ?

You can declare function with __declspec( dllexport ) modifier:
__declspec( dllexport ) void func();

Another way is to include function name into EXPORTS section of a module-definition (.DEF) file:

;MyDll.def : Declares the module parameters for the DLL.

LIBRARY      MYDLL
DESCRIPTION  'Some description'

EXPORTS
    MyFunction1 private
    MyFunction2 private