This is a 4 pins I2C 5-3V logic level converter. It is designed specifically for I2C interface pin set (that is why it have 4 pins). It can convert 5V signals to 3V and vice versa.
This converter also can convert 5-3V signals for other applications, not just for I2C devices. You can use SCL & SDA pins set to convert between 5-3V and vice versa for other applications such as digital sensor signals.
AVCC connected to 5V system power supply
ASCL connected to 5V system SCL
ASDA connected to 5V system SDA
Connect AGND to 5V system GND
BVCC connected to 3V system power supply
BSCL connected to 3V system SCL
BSDA connected to 3V system SDA
Connect BGND to 3V system GND