Many English learners have trouble reacting to the common English greeting “How are you?”. But before you answer the question you have to think about what the question really is.
Western and especially American culture is very individualistic. Everyone lives in the same society but value their individual thoughts and feelings very much. But no one wants to be selfish and always think about themselves. So when they ask “How are you?” it is a polite way to show that they are acknowledging you and think that your feelings are important to them.
So we usually answer “Fine / OK / Not bad / Can’t complain” something that is slightly neutral but generally good. We appreciate that someone asked us about our feelings but we don’t want to bother that person with the problems of our person.
If you say “Not so good / Horrible / Don’t even ask” this could burden the other person with your problems. This is fine with close friends and family, but could make you look weak or needy in front of coworkers or strangers.
If you say “Great / Awesome / Best day of my life” again it is fine with close friends but in other situations you don’t want to brag about your good mood. Maybe the other person isn’t happy.
So we usually answer something like: “Fine. Thanks. How about you?”
Fine (I’m generally good and not in a mood or situation that you have to worry about.)
Thank you (I appreciate you being concerned over my feelings.)
How about you? (I am also concerned about your feelings.)