async and await in C#

AsyncExplain.cs

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

namespace AsyncExplain
{
    class Program
    {
        public static void Main(string[] args)
        {
            Go();
            Console.ReadKey();
        }

        static async void Go()
        {
            var sumTask = ComputeServiceAync(3, 5);
            Console.WriteLine("Hello World!");

            //等待返回的task执行完成，因为我们需要用他的结果(Thread Block在这里，直到完成任务return结果
            var sum = await sumTask;
            Console.WriteLine(sum);
        }

        static Task<int> ComputeServiceAync (int a, int b)
        {

            var t =  Task.Factory.StartNew<int>(() => {

                Thread.Sleep(10000);
                return a + b;

            });

            //T代表一个正在执行的Task
            return t;
        }

    }
}