There are lots of write-ups for line follower robots, but they usually are complicated. First, the beginner is expected to learn a new microcontroller like a Basic Stamp or Arduino. Next they need to interface it with some servos which need to be modified for continuous rotation. Pratheek does away with that mess in his robot tutorial . All logic is controlled by transistors and the motors are simple electric ones with gear reduction. This project is well documented and includes lots of pictures.