User1120430333 posted
public StudentAddress StudentAddress { get; set; }
public Grade Grade { get; set; }
Those are objects within the Student object.
To access the properties of the objects in student you would have to address like this.
var student = new Student();
student.StudentAddress = new StudentAddress();
student.Grade =new Grade();
student.StudentName = "jasshvalik";
student.StudentAddress.Address = "no where";
student.Grade.TheGrade = "F";
OO is OO .NET of Java.
https://alfredjava.wordpress.com/2008/07/08/class-vs-object-vs-instance/