Namespace in C#

using System;

using first_namespace;

using second_namespace;

namespace first_namespace

{

    class classA

    {

        public void function()

        {

            Console.WriteLine("Inside first_namespace");

        }

    }

}// first_namespace end

namespace second_namespace

{

    class classB

    {

        public void function()

        {

            Console.WriteLine("Inside second_namespace");

        }

    }

}// second_namespace end

class TestClass

{

        static void Main(string[] args)

        {

            //first_namespace.namespace_1 f1 = new first_namespace.namespace_1(); // without (using) keyword

            //second_namespace.namespace_1 s1 = new second_namespace.namespace_1();// same classes name exist

            classA f1= new classA();// with (using) keyword

            classB s1= new classB();// same classes names doesn't exist

            f1.function();

            s1.function();

            Console.ReadKey();

        }

   

}