This is a question that people ask their family members when they get home from work. You don't ask it immediately when you walk in the door. Instead, you ask this question to signal that you want to start a conversation with them.
In many families, it's expected that you'll ask it each day. If you don't, your husband, wife, or child might get mad and say:
You didn't even ask me how my day was!
If someone asks you how your day was, you should tell some short stories about things that happened to you that day.