Beginner question: classes and constructor code?

So I've read this section a few times and it is not going in. I understand declaring regular variables, but this page in my book is talking about "public class MyNumber" then later goes on to say MyNumber numb = new MyNumber, what is the purpose of this and what is going on? Why can't they just stick to int a = 123, what is the point in all this new class and horrible syntax?