Hey Eric,
this should be rather easy. You already have CNC experience.
You open your favorite CAD/CAM program, create a 3D model of whatever you want to mill, select the Onefinity Post processor, export the toolpath as g-code to a USB stick (needs to be formatted with FAT32, NTFS or ext4 – support for modern exFAT is not installed¹ on the Onefinity Controller 
), insert the USB stick into the Onefinity Controller, click on the “Upload a new G-code program” icon, select the file, switch the router on, and click on the “Play” icon.
If you want to watch videos, you know where the OnefinityCNC youtube channel is.
There you can
- Learn how to load a g-code program on the Onefinity
- Learn how to use the Touch Probe
- Watch all the other “Support” videos.
1. – would become available via fuse on the older Raspberry Pi OS version found on Onefinity controller by doing ‘apt-get install fuse exfat-fuse exfat-utils’