Gas sensors are widely used in manufacturing Industries. There are wide varieties of gas sensors available. The gases like co, co2, H, o2 etc can be sensed as per the requirement. The gas sensor board gives two kind of output normally analog vot and digital output, The Analog output varies in the range of 0-5V range. The board needs +5V power supply. A pre heating is necessary to get the sensor. Coil detection the gas air its vicinity. This process take around 500 to 600MA of current. The power supply rating need to be consider when interfacing with microcontroller etc. The digital with a resistor pot. An LED indication helps you to observe the trigger of threshold level.
You can test this i-labz gas sensor board by connecting the +5V and Gnd connection. Wait for 1 to 2 minute to get sensor element to heat up blow the air or exhell the air on the sensor. Measure the Analog output of the sensor using multimeter in DC Voltage measurement mode. Observe the increase in DC voltage as you exhell the air on the gas sensor.