1. Used alone (with a questioning facial expression) to ask someone how they are or how things have been going. English = 'How are things going?', 'How have you been?', and so on.
2. Used alone in answer to the question/greeting "How are you?" to mean: "I've been well for some time", "Things are going fine", "Things are going great”, "Things are going well”, “Everything has been good for some time", "Fine (for some time)", etc.
3. Used alone in response to a question or greeting to mean that everything is fine or that you have experienced no problems. English = good, well, fine.