How do I tell the machine where I fixtured the piece of material to be machined ?
This is in fact machine-dependant. Obviously the machine does not know where to start: you will have to tell by setting the workpiece zero point. DeskProto makes that easy by using the left-front-top corner of the material block as zero point. So on most machines you can just move your tool to that position and tell the machine to use that position as workpiece zero point. Please consult your machines manual or your dealer for more help on this subject.