Not sure if this is what you're asking, but anyway...
You use classes to model the business logic. Classes are also great for reuse. For example, when starting a big programming one of the most important things you need to do is come up with a datamodel. For example, whe you build a hotel booking system, you'll have guest, booking, room, hotel and more tables. Each of these tables could then be a class that you use. For example, properties in the guest class would be firstname, surname, id number, address etc etc and methods would be create new, update, delete and more. Like i said, this is great for avoiding duplication of code, promoting reuse, making your code easier and clearer to understand and also for seperating the business logic from the presentation logic..
Is this what you wanted to know?
