When you hear a loud noise like a siren, it means something important is happening. Firefighters have sirens that make a loud sound and lights that flash to let everyone know they are in a hurry to help people.
When you see or hear these sirens, it is very important for cars to move out of the way so the firefighters can get to where they need to go as fast as possible. This helps keep everyone safe. Just like when you play, you stop and let others go when they really need to hurry!