PUBLIC MARKS from kmwang with tag win32

How do I call a DLL or Win32® API function from my C# code if the function has a string (char*) output parameter? I can pass a string for an input parameter, but how do I get the returned string? Also, how do I call functions that require a struct or a callback, like GetWindowsRect and EnumWindows? I'm trying to convert from C++ and MFC, and I can't cope!