Okay kiddo, so a staff officer is someone who helps the boss make important decisions. They're like the boss's helper, making sure things go smoothly and everything gets done on time.
Let's say we're playing a game of pretend where we are running a lemonade stand. I'm the boss and you're the staff officer. Your job is to help me decide how much sugar we need for the lemonade, how many cups we need, and who will serve the customers. You help make important decisions and give me advice.
In real life, there are staff officers in the military and in businesses too. They help the leaders of those organizations make important decisions by gathering information, analyzing data, and giving recommendations. They make sure everything runs smoothly and the boss doesn't forget anything important.