Ground Control Station communicates with the ArduPilot sending MavLink messages and commands. This is a good tutorial explaining what is MavLink and how to deal with it. Also, you’ll need a common message set specification which is available here. You’ll need to publish GLOBAL_POSITION to the /mavros/global_position topic. If you don’t know how to do it, you can read this thread dedicated to publishing to the topics.
As I said before, to calibrate ESC you can refer to this thread or use MAVProxy. Hope this will help.