How to map Win32 types to C# types when using P/Invoke?

Question

I am trying to do something like this in C#. I found out how to call Win32 methods from C# using P/Invoke from this link. However I met some difficulties in implementing P/I

Answer 1

[DllImport("Pdh.dll")]
    static extern Int32 PdhOpenQuery(string szDataSource, 
        IntPtr dwUserData, ref IntPtr phQuery);