A traffic light is a signal for cars and people. It has three colors: red, yellow, and green. The red light is at the top. Red means 'stop'. Cars must stop. The yellow light is in the middle. Yellow means 'wait'. The light will change soon. The green light is at the bottom. Green means 'go'. Cars can go now. Traffic lights are very important for safety on the road. They help people and cars move safely.