Pixhawk 4 for the Newbie

I did a google search “where to start with Pixhawk 4” so here I am. I’ve built from Hobbyking components a couple of 250 quads for my kids. They are very basic and the flight controller is/was a CC3D. But I have in mind a new project where I’d like to have GPS position hold and the ability to set a mission and set way points for the drone so I can photograph locations on my small hobby farm. Pixhawk looks to be an ideal setup. However from an outsider looking in, it’s not so clear to me. I would be very grateful if some could point me in the right direction of where to start the process of understanding Pixhawk and what is needed to do what I’d like to. Perhaps it is as simple as pointing me to an already written description/website as where to start I don’t mind.