If it's someone that you know, then you literally tell them how you're doing. Unfortunately, here in the U.S., when we are just walking down the streets(or in stores,etc...), we say phrases like"how you doing?", "how's it going", and "what's up?" to complete strangers alot, as another way of just saying "hello", because we really don't want to know about a complete stranger's personal life. I don't know why we say "How you doing" or "what's up" or "how's it going" to strangers, but we do. So we just usually answer "good/pretty good" if we are in a good mood, or we answer "alright" or "ok" if our day has been "ok", or we answer "I'm still alive"(meaning I'm having a bad day, but at least I'm alive) when we have alot of negative things on our minds. So unless we want to start a conversation with someone, we just briefly reply with a short answer and then we continue doing whatever we were going to do....It sounds rude but it's really not, because It is very common for guys to say it to other guys as an expression of hello. Now when a man aproaches a woman, we commonly say "hello" with a very sincere voice that almost also sounds like a question. And then we try to gently compliment them about their clothes or shoes, or hair, when we want to try and start a conversation with them. But never go up to a woman that you don't know and tell her how good her body looks haha.... But this is all just my opinion of everything, so I hope it helps you understand a little better.... When I was reading about the Chinese culture, it says that it's only common for friends to ask each other "ni3 hao3 ma" (how are you?), so it is completely different then how we often use that question as a form of expression. But that's good, because when you ask someone "how are you", you should really want to know. :)