To best use an Auto Pilot, you must think about it being a "Controller" (like a Thermostat or Car Cruise controller).
As Kloudie1 points out, you need "sensor feed back" to the Auto Pilot controller.
Feed back sensors to my ST6000+ Auto Pilot.
1) Rudder position or Reference
2) Flux Compass Bearing
3) GPS location, chart plotter, and sometimes wind speed (optional course tracking )
4) Sea State ( Human sensor that has to be preset or hand inputted)
Finally, and this an often overlooked requirement.....
Tuning the Auto Pilot for sensitivity to your Sensors and boat rudder size.
Jim...
PS: Kind of complex, but once "Tuned" a marvelous boat device.