Java构造方法 第三条没明白 怎么写啊

如图所示
我的思路是
1 person类里写Student st= new Student (); 2 Student类里写一个构造方法 里面写上一个局部变量赋值？ 3 Person类成员方法里写 st.age(18);？啥叫成员变量的成员放法啊，这步怎么调用不懂4 另写一个入口类p.成员方法名？？
实在没明白

1、Person 类

public class Person {

    private Student student;

    public Person() {}
    
    public Person(Student student) {
        this.student = student;
    }

    public Student getStudent() {
        return student;
    }

    public void setStudent(Student student) {
        this.student = student;
    }
    
    public String getStudentName() {
        if(student == null) {
            return null;
        }
        return student.getName();
    }

    public static void main(String[] args) {
        Student student = new Student("carl", 20);
        Person person = new Person(student);
        // 在 Person中的 getStudentName 方法中，会调用Student类型成员变量 name
        System.out.println(person.getStudentName());
    }
    
}

2、Student 类

public class Student {

    private String name;

    private int age;

    public Student() {}

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

写个继承关系，在子类中实现方法