Don't worry about this for the exam because wait, notify and notifyAll is removed from the exam.
When two or more threads are accessing the same object, just like a bank account, wait and notify are used. One
thread withdraws money from that account, two other threads should wait until the account is released by that thread before they can withdraw or add money to the account. When the thread finishes its withdrawal, it notifies one thread or notifies more than one thread by notifyAll() not to wait.
For more detail about this thread issues, I would recommend you to read any editon of How to Program in
Java by Deital and Deital. This book should be available in any public library.