Culture shock1

I don't know why i pay tip if i eat food in restaurant because we don't have tip culture. So, I felt to begrudged because minimum tip's percentage is 15%. I still don't  understand. I heard why America has tip culture because salary is so cheap and waiter get tip. Before, I think, boss get all tips but, worker get tips. It is interesting but, I don't like that. Maybe, I will be adapted soon. That is my first culture shock.