This product is a fully functional inexpensive 3.3V /5.0V (jumper selectable) FTDI Cable using the standard 6-pin female header on the bottom of the board. This is a board and cable utilizing the standard FTDI FT232RL USB to serial IC. Compare at $19 for other FTDI cables The pinout of this board matches the FTDI cable to work with 5V/3V Arduino board as well as matching the FTDI pinout for the ESP8266 breakout boards such as the Adafruit Huzzah Board. It can also be used for general serial applications. The major difference with this board is that it brings out the DTR pin as opposed to the RTS pin of the FTDI cable. The DTR pin allows an Arduino target (it makes no difference to a ESP8266 to auto-reset when a new Sketch is downloaded. This is a nice feature to have and allows a sketch to be downloaded without having to hit the reset button. This board will auto reset any Arduino board that has the reset pin brought out to a 6-pin connector. The pins labeled BLK and GRN correspond to the colored wires on the FTDI cable. The black wire on the FTDI cable is GND, green is CTS. Use these BLK and GRN pins to align the FTDI basic board with your Arduino target. This board has TX and RX LEDs that make it better to use than a standard FTDI cable. You can actually see serial traffic on the LEDs to verify if the board and your software is working. This board was designed to decrease the cost of Arduino development and increase ease of use (the auto-reset feature rocks!).