The DigitalOutputStart VI is selectable in the StartPhidget.vi, which is the same for the Close VIs.
As you probably expect, the LEDForwardVoltage, DutyCycle, and Hub Port parameters don't really make sense for your specific application, and are included since they are used by other Phidgets in the DigitalOuput class. These can be safely ignored until you have a Phidget that uses them.
Here is a diagram of how to access the relays on your device: