I went to CVS Pharmacy to buy newspaper and got the usual 'How ya doin?' greeting from the cashier. When I moved here, I actually don't know what's the proper answer for that question. I am used with 'I'm fine, thank you' because that's how we usually replied to 'How are you?' in our country. Then, another usual greeting 'What's up?' (in short for what's happening to you lately?) which I usually replied with nothing much. In my country, you seldom hear greetings like these between two strangers because it starts a conversation with someone that's not a close friend. Disclosing things that happened recently to someone is most of the time exclusive between friends/relatives. You don't ask someone that you don't know with 'what's up?' and 'how ya doin?", because for them it's a private thing and should not be talked about in public. But here in USA, they are social tools to initiate a conversation and not a sincere concern on what's happening to you or how are you doing in terms of your health for example. You can be polite to decline by saying, 'I'm good' and end up with 'thank you' otherwise if you want to engage more with the conversation, you can add 'How about you?" or just simply "you?". It takes time to feel at ease with these mediums that initiate conversation. You will hear and receive these greetings everywhere you go. As the saying goes, when in Rome, do the Romans do.