Delegate in C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

public delegate void En(string message);
public delegate string De();

namespace MQueue
{
    class Program
    {
        static void Main(string[] args)
        {
            MQueue myqu = new MQueue();

            En a;
            De b;

            a = new En(myqu.enqueue); //keep method enqueue in delegate En
            a("Hello How are you?"); //use it like -> myqu.enqueue("Hello How are you?");
            a("I'm fine, Thankyou");
           // myqu.enqueue("Hello How are you");
           // myqu.enqueue("I'm fine, Thankyou");

           b = new De(myqu.dequeue); //keep method dequeue in delegate De


           string text;
            while (myqu.isempty() == false) {
                text = b(); //use it like -> myqu.dequeue();
                Console.WriteLine("{0}", text);
            }
        }
    }

class MQueue
    {
        ArrayList queue;
        public MQueue() { queue = new ArrayList(); }


        public void enqueue(string message)
        {
            queue.Add(message);
        }
        public string dequeue()
        {
            string message = (string)queue[0];
            queue.RemoveAt(0);
            return message;
        }
        public bool isempty()
        {
            return queue.Count == 0;
        }


    }
}