The red line is like the line you draw on paper to separate things. But instead of separating paper, it separates a place called a train station from the place where the train goes on the track. The red line is special because it only goes to the train stations with red signs, and it doesn't go to the train stations with other colored signs. When you get on the train, make sure to look for the red line signs so you know you're going the right way!