You have to give it velocity by accelerating before you can move it. There is a document in the doc folder that goes into some of the basics of flying on the ground map. Beyond that, you will have to read the rules in TW to know how to use it.
To start with a dropship grounded, open up the customize unit window in the chat lounge and go to the deployment tab and set its altitude to zero. Make sure you use a map that has enough flat open space to actually place it.