"How are you?" is a nice question. It's a friendly way that people in the USA greet each other. But "How are you?" is also a very unusual question. It's a question that often doesn't need an answer. The person who asks "How are you?" hopes to hear the answer "Fine" which isn't really an answer. It is simply another way of saying "Hello" or "Hi".
Sometimes, people also don't say exactly what they mean. For example, when someone asks "Do you agree?" the other people might think, "No, I don't agree. I think you are wrong." But it isn't very polite to disagree so strongly, so the other person might say "I'm not sure." It's a nicer way to say that you don't agree with someone.
People also don't say exactly what they are thinking when they finish talking with other people. For example, many talks over the phone finish when one person says "I've to go now." Often, the person who wants to hang up gives an excuse: "Someone is at the door." "Something is burning on the stove(炉子)." The excuses might be real. Perhaps the person who wants to hang up simply doesn't want to talk any more, but it isn't polite to say that. The excuse is more polite, and it doesn't hurt the other person.
Whether they are greeting each other, taking about an idea, or finishing a talk, people don't say exactly what they are thinking. It's an important way that people try to be nice to each other. It's part of the game of language.
