Is/ought gap and fact/value distinction and the naturalistic fallacy.

Hey guys i am self teaching A2 AQA philosophy revising for my exams next month and so sometimes just reading the description fails to get through. I was wondering if anyone could explain in real simple terms perhaps with an illustration how they all work as they are making me hate meta ethics.

It's important to seperate the is/ought problem from the naturalistic fallacy.

Is/ought: you cannot infer from some 'is' fact to some 'ought' fact.E.g. it may be the case that 'cancer is painful' but we cannot infer from this that 'we ought to treat cancer'. There seems to be a problem moving from a descriptive statement to a prescriptive statement. Why does x being painful imply that we ought to try and cure x?

Naturalistic fallacy: You cannot define moral terms in naturalistic terms. You cannot define goodness in terms of pleasure because they don't mean the same thing. How do we know this? Because if they meant the same thing then we would be contradicting ourselves by saying 'x is good but not pleasurable' in the same way as we would contradict ourselves by saying 'John is a bachelor but isn't an unmarried man'. But it seems that we don't contradict ourselves in such a way. Therefore they don't mean the same thing and so moral terms cannot be defined in naturalistic terms. This is Moore's famed open question argument.