Okay, little buddy! When we're talking about trains, we need to understand their signals. Think of these signals as special signs that tell the train what to do. Let's break it down:
1. Green Light: Imagine the green light is like a big friendly 'GO!' The trains love this green light because it means they can start moving. Just like when you go to the park and the light turns green, it's your turn to run!
2. Paddle Up: Now, if someone holds a paddle up, it's another way of saying 'GO!' The paddle is like a big flag. It tells the train, 'Everything is good, you can go!'
3. Whistle: When you hear a whistle, it's like a train's horn saying 'Woohoo, it's time to go!' It's not the same as a car horn. This whistle helps everyone know the train is ready to move.
So, when you see the green light or a paddle up or hear a whistle, just think 'time to go!' because the train is ready to chug along!