This is soil moisture sensor module. PCB based small but effective probe and complete module with connecting wires. Two pads of probe acts as veriable resistance as more water means better conductivity and resistence reduces and high output. Just connect vcc and gnd in module and it will give two output one is analog another is digital.
Trimpot in the module is used for tharshold setting for moisture level sensing, digital will give high or low depending upon level set for amount of moisture. Analog pin will be used for controller or Arduino ADC pin to determine the moisture level.