Sensors are components with which the Robby perceives its environment. With them he can see something or feel something.
The movable bumper (with buttons)
When the bumper is pressed, 2 buttons inside the Robby detect if the bumper was pressed left, right or center.
The picture on the top right of the First Coding App screen shows you on which side the bumper was pressed: left - center (both buttons pressed) - right. You can react to these events in a program and, for example, avoid an obstacle
The "eyes" (the infrared track sensor)
On the bottom side the Robby has "eyes". With them he can distinguish a black track from a light background and thus follow a track. The "eyes" consist of an infrared transmitting diode that emits invisible infrared light and two infrared receiving diodes that detect infrared light reflected from the ground. Since a white background reflects more infrared light than a black background, the Robby can detect a black track on a white background, for example, and follow the track.
The image at the top right of the First Coding app screen tells you whether the "eyes" detect light or dark.