Question: 

What does the driver do on their end to register a DT unit?

Answer:

The unit should prompt the driver to enter a truck number as soon as it’s up and running. Once they enter the truck number that is assigned to the driver into the field, they can press the green arrow. Leave the “Optional Registration” field blank and press the green arrow again.

As soon as this is done you should be able to see the truck in FleetWatcher.