Class methods and instance methods - when/when not to use them?

Question

I was wondering when and when not to use class methods and instance methods. I need some practical examples. I am really confused. Another question: can't we do exactly the same things with instance methods that we can with class methods?

Answer 1

Class methods: The method isn't tied to any specific object. In a way it acts like a free function in the class's namespace. No 'self' pointer. For instance [UIScreen mainScreen] is a class method because there's only one screen and there's no need to care about multiple 'screen instances'.

Instance method: Tied to a specific object.

This applies to most OO languages, not just obj-C.