how does work thread

class Threading1
    {
        static void Main()
        {
            ThreadStart job = new ThreadStart(ThreadJob);
            Thread thread = new Thread(job);
            thread.Start();

            for (int i = 0; i < 4; i++)
            {
                Console.WriteLine("First Thread: {0}", i);
                Thread.Sleep(1000);
            }
        }

        static void ThreadJob()
        {
            for (int i = 0; i < 8; i++)
            {
                Console.WriteLine("Remaining Threads: {0}", i);
                Thread.Sleep(500);
            }
        }
    }