Okay, let me explain it to you like you are 5 years old!
Imagine you are a captain of a pirate ship, and you have a crew to help you sail the ship. However, as the captain, you can't do everything on your own, so you need some help. Some of your crew members give you advice and help you make important decisions, while others help you with daily tasks like hoisting the sails or scrubbing the deck.
This is where the concept of staff and line comes in. The crew members who give you advice and help you make important decisions are called staff. They don't have as much authority as you do, but they have special expertise in specific areas, like navigation or weapons.
On the other hand, the crew members who help you with daily tasks and directly carry out your orders are called line staff. They report to you directly and are responsible for completing the tasks you assign them.
So, in short, staff members are like advisors who help you make important decisions, while line staff are the crew members who carry out those decisions and complete daily tasks on the ship. They both work together to make sure the ship runs smoothly and everyone is safe.