Ok Philippe,give me a moment and I'll get you the files you need.
Step 3 works like this. You take your gcode that you just posted and you run it in the G-code program I will send to you. It essentially controlls the motion of the machine. You can do a number of things with it, namely:
1) preview a file before you cut. This is important and you want to check your depth of cut by viewing the footpath from the side and front angles.
2) set up and configure your machine for important stuff like acceleration rate, units, feed rate, and a multitude of configuration parameters that will define the cuts you make.
3) run the code which is in the form of an ncd file.
But before you get to cutting it's important that you have everything on the machine nice and clean and lubed. Don't worry about mounting the z axis just yet. You need to do a wire check first and make sure everything functions properly. Then if you have motion control, square up the z before you put it on with a dial indicator. Then you'll have to install the z on the gantry and square it up again. Finally you'll have to install the spindle and square that up for good measure.
But since you are looking for free programs and such I highly recommend Scorchworks. F-engrave, Gcode ripper, and Dmap2gcode. But you will also need a free program for your cad. There's plenty of options out there but I would suggest a simple 2d cad program for drawing lines, arcs, spline, and primitive shapes like rectangles, ovals, and nourishment shapes. If you use the free stuff from Scorchworks, it's important that your cad software is compatible with dxf files.
That should give you plenty to do while I get that file for you.
Now there's some information I need from you to be shire this will work.
1) Are the motors servo or stepper?
2) Is the amplifier box that drives the motors connected to a card in the computer fitted to an IS A SLOT or a PCI slot?
What software you use to control machine motion depends critically on these two factors.
I hope I can help.
Alex