how to insert data in many to many relationship mvc4

public class Student
{
    public int StudentID { get; set; }
    public string Name { get; set; }
    public virtual ICollection<AssignedCourseData> Courses { get; set; }
}

public class CourseViewModel
{
    public int CourseID { get; set; }
    public string CourseDescripcion { get; set; }
    public virtual ICollection<Student> Students { get; set; }
}

[HttpPost]
    public ActionResult Create(Student student)
    {
        if (ModelState.IsValid)
        {
            var student = new Student { Name = student.Name };

            AddOrUpdateCourses(student, student.Courses);
            db.Student.Add(student);
            db.SaveChanges();

            return RedirectToAction("Index");
        }

        return View(userProfileViewModel);
    }

    private void AddOrUpdateCourses(Student student, IEnumerable<AssignedCourseData> assignedCourses)
    {
        if (assignedCourses != null)
        {
            foreach (var assignedCourse in assignedCourses)
            {
                if (assignedCourse.Assigned)
                {
                    var course = new Course { CourseID = assignedCourse.CourseID };
                    db.Courses.Attach(course);
                    student.Courses.Add(course);
                }
            }
        }
    }