Hey kiddo! Do you know how soldiers in the past used to shoot their guns? They would stand in a line and shoot one at a time, so they had to wait for their turn to shoot. But then they learned to shoot all at the same time, which is called a "volley fire".
Think of it like a game of catch. Normally, you have to wait for your friend to throw the ball back to you before you can throw it again. But volley fire is like when you and all your friends throw the ball at the same time.
It's good for soldiers because it makes the enemy think there are more shooters than there really are. It's also helpful because the enemy might not know where the shooting is coming from, so they can't aim their own guns as easily. It's an important tactic for soldiers and has been used in many battles!