Use this module to connect two devices of different digital voltage levels. For example: connecting an Arduino (5V device) to an ESP8266 (3.3V device).
This module requires you to supply it with power from both the higher voltage level and the lower voltage level. Connect the higher voltage source to pin "HV" and its ground to pin "GND" near the "HV" pin. Also connect the lower voltage source to pin "LV" and its ground to pin "GND" near the "LV" pin. For example, if you were connecting your Arduino (5V signals) to an ESP8266 (3.3V signals), you would connect the "HV" pin on the module to the 5V supply pin on your Arduino and the "GND" pin near the "HV" pin to the "GND" pin on your Arduino. Then, you would connnect the "LV" pin on the module to the 3.3V power source that is supplying power to the ESP8266 and connect the "GND" pin near the "LV" pin to the 3.3V power supply's ground. You would then connect the signal pin from your Arduino to one of the signal pins on this module (for example, pin "HV1"), and then you would connect the desired signal pin on the ESP8266 to the corresponding pin on this module ("LV1" if the higher voltage signal is connected to "HV1").