You drive the Ranger around until it sees an obstacle(ultrasonic's the best!), and if it sees one, it will stop, turn on red lights, and beep until you help it. The mBot will hang out with you, alerting you if the Ranger sees an obstacle(in case the Ranger is far away!) by also turning on red lights and beeping. The mBot's alerts can be turned off by pressing the on-board button. Oh, and using a potentiometer in port 6 lets you adjust the speed.