I have a Cape Horn windvane and an old Navico 5000 which we call Otto. It steered hundreds of miles offshore when I hit the frustrating calms, and it put up with swells and rolling and what not. It should only be used when motoring in calms, or in very docile sailing conditions, although it will drain your batteries if you don't have additional power supply such as solar panels, wind generator, etc.
The Ottopilot should be about 90 degrees from the tiller, attached to a wooden block or something similar on the aft deck. You put a pin on your tiller where you stick the arm of the pilot, et voila, you have your tiller slave. You usually have a button for a fixed course, then 2 others for adjusting the course one degree at a time, port and starboard.
This may be way too basic information for you, but there's nothing to it really, except that you need to connect the wires properly and have that right angle to the tiller.
Maybe the other guys can give you a more sophisticated answer here, for me it was a pretty straight forward deal.