Sometimes good manners in one place are bad manners in other places.
If you are a visitor to Mongolia and some friends ask you to eat with them, what kind of manners do they want you to have? They want you to give a loud "burp"(打嗝)after you finish eating. Burping will show that you like your food. In some countries, if you give a loud burp, you should say, "Excuse me, please. "
In many places people like to eat together. But in some parts of Polynesia, it is bad manners to let others see you eating. People show their good manners by turning their backs on others while they eat.
How about visiting a friend in Arabia? Do you walk past every house? No, you shouldn't do that. Do you know why? You must walk behind each tent till you reach your friend's tent. It's because if you are invited into a tent, you cannot say "no". If you do, you'll be very impolite.
Manners are different all over the world. But it is good to know that all manners begin in the same way. People need ways to show that they want to be friends.