You control the trains by clicking on them, and dragging to the track that they have to go on. The train will move on another track that is instantly built when you let go of the screen, and that track will lead to the ultimate track. Each track has a number assigned to it, and each new train will have a number displayed above it which indicates the track it has to travel to. You earn points when a train exits the screen on the correct track. If not directed to the right track, and a train leaves the screen on that track, you will lose a different amount of points. This number depends on the combo that you have built up.