The little help that there is reads:
# Usage : Move Group or groups to within the safe area starting from 0,0 and on the 0 plane then run the contour script

I find it works a little better if the bottom left corner of the part is not at 0,0, but rather a little more than bit diameter to the right and up.

I tested it with a 6mm bit, and offset it 7mm. stepover% should be less than 50% otherwise the finish will be very rough.

You also need to select the whole object and create a group.

set Z zero at the top of the material, 61mm thick in this case.

Results may not be what you expect, SketchUcam is focused on 2.5D work and the 3D module needs a lot of work.
I believe a better solution is to design in Sketchup, export to STL file, import that into PyCAM and use that to generate the Gcode.


settings I used


SketchUcam is much better at 2.5D cuts, which are quite versatile (unless you want curved surfaces)