When someone says, "How are you?", you can answer, "I'm okay", which means I am allright, not good or bad. You can also say, "Not bad" or "I have been worse" or "I've been better". If you know the person well, you probably would be more honest with your answer. If you really don't know the person, "fine, thank you" is the normal answer.

if you are not fine ... you can just say when asked "how you are?".. i am not very well today i am not fine i have had a bad day today has not been a good day.. i am not well i feel bad if you are not good because your sad you can just say that i am sad i am tired.. you don't have to say you are fine when you truly aren't.. i am angry

I'll answer (I'm fine) even when I'm not,, especially when I'm not.

Unless the person asking the question is close to you, there is no point in giving any other answer other than 'I'm OK / Good / etc'. Because, most people don't expect to hear any other answer. It's just a formality to ask someone how they are. It's similar to 'Ni hao ma' or 'Zui jin hao ma' in Chinese, I guess. If the person asking the question is a close friend or a relative, then you can feel free to express your feelings or emotions at that time the question was asked. Yeah, it gives a feeling that we live in a fake world where people don't mean what they say, sometimes :-)

Probably not. Why lie about such small things?