How shall I export FreeCAD CAM Job to bCNC?

[HKPhysicist]

Hello Dear CNC Experts,
I am completing my first CAM exercise in FreeCAD v1.0. It is a big success. Here are the lessons:
https://blog.freecad.org/2023/11/24/tutorial-getting-started-with-the-path-workbench-part-one/

The last step is to export the CAM Job to GRBL processor.
Now my questions are:

1. What should be the file format for bCNC?
2. Which coordinate system should I choose?

Thanks so much for your help. I am going to create the simple CAM Job for my plastic enclosure. ^^