Hey Charles,
wow, you’ve already received and built the machine and only then you start to think about that 
. But congratulations for your new machine!
The advice is actually to start at the latest when you order the machine, because learning to use a CAD/CAM program can take some time. But never mind, go ahead.
To answer your question: You need a CAD/CAM program in which you create an object or open one that you got from somewhere else, and then export it as a g-code toolpath, selecting a postprocessor. This then results in the .ngc file that you load onto the Onefinity and run.
Here are the infos from the FAQ section that will help you:
- What CAD/CAM software can be used to make gcode files for the Onefinity CNC
- What is a Post Processor, What does it do, And why do I need one specificly for my Onefinity
Welcome to the forum!