I want to try out this API function:

ULONG WINAPI GetAdaptersAddresses(
_In_ ULONG Family,
_In_ ULONG Flags,
_In_ PVOID Reserved,
_Inout_ PIP_ADAPTER_ADDRESSES AdapterAddresses,
_Inout_ PULONG SizePointer
);

How do I use that in VFP?

See https://msdn.microsoft.com/en-us/library/windows/desktop/aa365915(v=vs.85).aspx for more detail