I2C Module has a inbuilt PCF8574 I2C chip that converts I2C serial data to parallel data for the LCD display.
These modules are currently supplied with a default I2C address of either 0x27 or 0x3F. To determine which version you have check the black I2C adaptor board on the underside of the module. If there a 3 sets of pads labelled A0, A1, & A2 then the default address will be 0x3F. If there are no pads the default address will be 0x27.
The module has a contrast adjustment pot on the underside of the display. This may require adjusting for the screen to display text correctly.