using System;

public class Program

{

    public static void Main()

    {

        var theString = "hello";

        var method = theString.GetType().GetMethod(

            "Substring",

            new[] {typeof(int), typeof(int)}); //The types of the method arguments

        var result = method.Invoke(theString, new object[] {0, 4});

        Console.WriteLine(result); //"hell"

    }

}