American people like to say "Thank you." when others help them or say something kind to them. People in many countries do so too. It's a very good habit (习惯). You should say "Thank you." when someone passes you salt on the table, or when someone says you do your work well, you buy 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, husbands and wives.
"Excuse me." is another short sentence they use. When you hear someone say so behind you, you know that somebody wants to walk past you and doesn't want to hit you.
It's not polite to interrupt (打扰) others when they are talking. If you want to speak to one of them, say "Excuse me." first, and then begin to talk. You should also do so when you want to cough or make some noise before others. Let's learn to say "Thank you." and "Excuse me.".
