The stand is designed to fit any gas sensor from MQ sensor. Thanks to it, the connection of the sensor is reduced to only three (instead of six) pins (VCC, GND, VOUT).
VCC- 5V power supply
VOUT- output signal
On board is also a place for a resistor that regulates the sensitivity of the sensor (in the documentation called RL). The resistor can be connected in two ways: horizontally and vertically.
The gas sensors are not polarized and therefore can be installed in any order, at each side of the board (four options available).