I want to know why make classes? if you can simply make methods in the main class?

Answer 1

in order to organize more effectively Your program. With classes, objects and methods you can split Your code into separate actions which are invoqued whenever you want.

Answer 2

It is bcoz of OOP features. if you don't want OOP functionalities then don't create any classes and implement everything in main class. Going ahead you might feel to use OOP as and when complexity of program increases.