The FTDI cable is a USB to Serial (TTL level) converter which allows for a simple way to connect TTL interface devices to USB. The I/O pins of this FTDI cable are configured to operate at 5V.
The FTDI cable is designed around an FT232RQ, which is housed in a USB A connector. The other side of the cable is terminated with a 0.1" pitch, 6-pin connector with the following pinout: RTS, RX, TX, 5V, CTS, GND (RTS is the green cable and GND is black).
This cable can be used to program your Arduino Pro, Pro Mini and Lilypad. For use with those boards, align the black and green wires of the FTDI cable with the 'BLK' and 'GRN' labels on the PCB.