culture shock? that's ok

I spend 2month in America. I'm so interesting.
In the U.S.A. people greet to each other with cheerful and bright manner even to the stranger as if they had known each other for a long time but in Korea, they have a lot of suspicion toward any stranger and they are considerably sober.In the U.S.A they have party once a week and they are used to with parties but party culture in Korea is not widely opened in our daily life and we are not accustomed to parties.In the U.S.A. the Dutch Pay is very popular but in Korea, normally one person pay for the dinner and the others buy the next time. so I'm really like America culture.