This is a RoHS compliant I2C Serial LCD Daughter board that can be connected to a standard HD44780 compatible 16x2 or 20x4 Character Display Module that supports 4 bit mode. All Character Modules sold on our site support 4 bit mode, and nearly all commercially available 16x2 and 20x4 line character modules support it too.
This board has a PCF8574 I2C chip that converts I2C serial data to parallell data for the LCD display. There are many examples on internet for using this board with Arduino. Do a search for "Arduino LCD PCF8574". The I2C address is 0x3F by default, but this can be changed via 3 solder jumpers provided on the board. This allows up to 3 LCD displays to be controlled via a single I2C bus (giving each one it's own address).