What’s the deal with serialization?

Today we’re going to talk about a basic, (but from time to time useful) feature of Java — serialization.
Let’s start with theory. So what is serialization?

To serialize an object means to convert its state to a byte stream so that the byte stream can be reverted back into a copy of the object

[Serializable Objects, Oracle Java Documentation]

OOP - how to do it right? - part 1

When I started my journey with Object Oriented Programming I quickly found out many tutorials and trainings, which showed how to use OOP structures in code. Unfortunately, most of them demonstrate only how to write your first own class, interface. How to create an object. All of this was about language “grammar”, about key words, the way how to create structures used in OOP, etc. Yet, somewhere authors lost the most important information to share - why we decide to do this instead of looking for other solutions? Why an interface contains nothing more than abstract methods? Why all of those are public? What for are those visibilities? And so on...