In this mode, the robot will wander around. It will go straight until detects something in its way, then it will turn or back up and go in some other direction. It will go indefinitely until you turn it off or the batteries go dead.
While your robot is going straight, place your foot in the way. The front sensors will detect your foot. The robot will stop and try to turn away from the obstacle.
When the robot is going straight again, block the robot's head with your hand to stop the robot. Make sure you don't get anything in the way of the front sensors. Even though the front sensors don't detect an obstacle, the motion control routines will detect an excessive load on the motors and the robot will think it is stalled. It will back up, and try to go some other direction.
Now pick up the robot from behind when it is going straight. When it is several inches off the floor, the robot will stop its motors. There are two sensors on the bottom of the robot that detect the floor. When the robot can't detect the floor anymore, it thinks it is about to roll off a ledge. The robot can't tell the difference between being picked up and peeking over a ledge so it will try to back up. Put the robot back down and it should be happy again.
The robot also checks for stalls and detections from the floor sensors during turns. During a turn, try picking up the robot or block its head with your hand to stop it and see what happens.
When turning, the robot checks the rear sensors for obstacles. This is because the rear end of the robot could bump something while it is rotating. Try putting your foot in the way when the robot is turning and see what the robot does.