American people like to say “Thank you” when others help them or say something kind of them. People of many countries do so, too. It is a very good habit.

    You should say “Thank you” when someone passes you the salt on the table, when someone walking ahead of you keeps the door open for you, when someone says you have done your work well, or you have bought a nice thing, or your city is very beautiful. “Thank you” is used not only between friends, but also between parents and children, brothers and sisters.

    “Excuse me” is anther short sentence they use. When you hear someone stay behind you, you know that someone wants to walk to past you without touching you. It's not polite to break others when they are talking. If you want to speak to one of them, say “Excuse me” first, and then begin to talking. You should also do so when you begin to cough or make any noise before others.