Can someone explain concept of ontomany, manytoone and manytomany when we need to use? In which situation? if we take an example like there is a Student, Exam and subjects class and below are the fields which we need to use, How we will create our model?

Each Student has the following fields:
Student Registration ID (Unique Identifier)
Student Name
List of enrolled Subjects
List of registered Exams
Each Subject has the following fields:
Subject ID (Unique Identifier)
Subject Name
List of registered Students
Each Exam has the following fields:
Exam ID (Unique Identifier)
Subject
List of enrolled Students

Want to understand the concept of manytomany, ontomany and manytoone.