Three scenes (red, blue and green) registered when the game is created. Only the first one starts; the others wait until you change to them. Press A, B or C to jump to each.
Each change is useScene().change(name): it starts the target scene and replaces the current one. It is asked for by name and not by function, which is what lets a scene arrive from anywhere, a chunk loaded later or a document read from disk, without whoever calls change having to hold it.