use of this in programming in c#

using System.IO;
using System;

class Student {
   public int id, age;  
   public String name, subject;

   public Student(int id, String name, int age, String subject) {
      this.id = id;
      this.name = name;
      this.subject = subject;
      this.age = age;
   }

   public void showInfo() {
      Console.WriteLine(id + " " + name+" "+age+ " "+subject);
   }
}

class StudentDetails {
   public static void Main(string[] args) {
      Student std1 = new Student(001, "Jack", 23, "Maths");
      Student std2 = new Student(002, "Harry", 27, "Science");
      Student std3 = new Student(003, "Steve", 23, "Programming");
      Student std4 = new Student(004, "David", 27, "English");

      std1.showInfo();
      std2.showInfo();
      std3.showInfo();
      std4.showInfo();
   }
}