When looking at the sensors from the same angle as the shop photo the pins, from left to right, are GND, Data, VDD. The red pads on the pinout diagram are the pads where the connector attaches to the boards!
They are digital sensors that give out a sequence of pulses - you can read the moisture level by hooking the data pin up to a GPIO and monitoring the frequency of the pulses (you can see how Grow does it here).