基础应用

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

namespace Threading
{
    class Program
    {
        static void Main(string[] args)
        {
            var t1 = new Thread(ThreadMain);
            t1.Start();
            Console.WriteLine("This is the main thread.");
            Task.Run(() => { Console.WriteLine("Runing in the second thread."); });
            Console.ReadLine();
        }
        static void ThreadMain()
        {
            Console.WriteLine("Runing in a thread.");
        }
    }
}

task与thread的异同（答案收集于百度）：

task是根据自己需要调用线程,thread就是个基本单位；
thread是单核多线程，task是多核多线程；
直接用Thread做多线程和用Task目前还是看不出太大的区别；
Task对象需要更多的内存，但任务运行的更快；
从网上百度了一个比较task，thread，threadpool效率的代码：

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

namespace Threading
{
    static class Program
    {
        static void Main(string[] args)
        {
            for (var i = 1; i <= 50; i++)
                TestTask(i);
            for (var i = 1; i <= 50; i++)
                TestThreadPool(i);
            for (var i = 1; i <= 50; i++)
                TestThread(i);
            Console.ReadLine();
        }

        private static void TestThread(int i)
        {
            Console.WriteLine("Thread {0} start.", i);
            new Thread(h =>
            {
                Thread.Sleep(5000);
                Console.WriteLine("-------------------Thread {0} end.", i);
            }).Start();
        }

        private static void TestThreadPool(int i)
        {
            Console.WriteLine("ThreadPool {0} start.", i);
            ThreadPool.QueueUserWorkItem(h =>
            {
                Thread.Sleep(5000);
                Console.WriteLine("-------------------ThreadPool {0} end.", i);
            });
        }

        private static void TestTask(int i)
        {
            Console.WriteLine("Task {0} start.", i);
            new Task(() =>
            {
                Thread.Sleep(5000);
                Console.WriteLine("-------------------Task {0} end.", i);
            }).Start();
        }
    }
}

由下图可见，thread相对速度要快一些。不知道这样比较是片面的，以后还要多多留意。