Cultural Shock 1

When I walked everywhere, Americans always say 'Hi' or 'How are you?' I heard first time, I was really embarrassed, because Korea doesn't have this culture. In korea, I have never spoken with stranger. So I thought why are they saying hello? I don't know who is she or he. Also, when I was eye contact with someone, someone smiled me.
For a long time I didn't adapt that culture, so I avoided saying hello and eye contact.
But now I can say 'Hello' and 'How are you?' when I meet stranger on the way or market.