You now have developed a complete project. Hopefully, you’ll remember how important it is to turn everything into classes. The use of test applications is very important to keep a large project under control.
But of course the way we went through this project step by step does not quite match reality. The author of this course knew exactly what needed to be done and in what order you could best tackle a problem, before you even started on this exercise. If you start on your own project that will be very different. It is very common that you need to change the classes that you made. Often, methods you really need are missing because you didn’t think of them before, and you will write methods which end up unused. That is, especially for a novice programmer, quite normal.
Only through experience you can learn to assess what features are really needed in a class. And even then you can not always predict them exactly.