The minimum you need in addition to the dll file is some documentation of the functions of that DLL, including the function names.
If you have that you can load the library with the LoadLibray function of Windows. Then use multiple calls to GetProcAddress to retrieve pointers to the functions you want to call. To actually call the function, you need to cast that pointer to a pointer to function with the correct signature, i.e. calling convention, return value, and arguments.
So your code will look something like this:
HINSTANCE hMyib = LoadLibrary (_T("MyLib.dll"));
if (hMyib == 0)
{
}
typedef int MyLibFunction (double arg1, int arg2);
MyLibFunction* pLibFunction =
(MyLibFunction*) GetProcAddress (hMyib , "MyFuncName");
if (pLibFunction == 0)
{
}
int retValue = (*pLibFunction) (3.14, 42);
If your library contains C++ code, things get more complicated as function names will be mangled (contain some addition characters that encode the signature of the function).
Hope that get's you started in the right direction.