The CreateDigitalOutput function creates an object which manages digital output for a particular pin on the IOIO board.
Put the number of the pin you wish to use in the pinNum parameter (Any of the 48 pins can be used as a digital output). The startVal parameter should contain a true or false value depending on what state you wish the pin to be in initially (Hi=true, Lo=false).
If you leave out the mode parameter the pin will be opened in normal mode where logic Hi = 3.3V and Lo = 0V. Setting the mode parameter to "OpenDrain" will enable a mode where logic Hi = Disconnected and Lo = 0V.
See http://github.com/ytai/ioio/wiki/Digital-Io for more details.