How exactly is Mission Planner communicating with Pixhawk?

Very new to the UAV scene and I’ve got an X8+ which is using Pixhawk. I’m curious as to how Mission Planner actually manipulates the altitude of a drone? Does it send a couple of bits or keywords? Is it sending a signal?

I’m interested in figuring out a way to control my UAV with SOFTWARE. Perhaps I wouldn’t try to move the UAV a huge distance, but if I could make a small GUI of arrow keys that could move it a couple of inches in the Y or X direction that’d be great.

Mission Planner v 1.3.31

Can someone point me in the right direction?

Mavlink Protocol, google it:)