The Motor service gui is being updated. It has been designed to support multiple motor controllers. This is nice, since there can be a little complexity in attaching a motor to a motor controller.
For example an Arduino can directly drive a simple 2 bit H-bridge connected to a DC motor. Or a motor shield can be used, which has its own motor port configuration. Other shields and bridges might have different configuration.
Adafruit Motor Shield
Arduino driving simple H-bridge