The First Challege - Line Following: This video shows the robot turning left in which if the left sensor sees black, and the other sensors see only white, it turns left. Then it proceeds to follow the line.
The Second and Third Challenge - Intersection: This video shows the robot following a line and reading an intersection in which it will proceed to either make a turn, or go straight. The robot is able to follow the line by using the sensors on the bottom of the robot. The sensors are able to detect the color of the line and adjust the speed of the motors accordingly.
This is another intersection/line following video.