Software

CAM

Sheet Cam Software
Free version available to use while you are getting accustomed limited to a hundred plus lines of G-code which is enough to cut out many projects that a DIYer may wish to do.  It takes a LINUX or Windows Computer.

You can also use Sketchup with a plugin but you will need to tweak the code to work with a plasma cutter and contend with menus that do not correspond to Plasma cutting at all well.
Sketchup With
Gcode PluginDesign

Inkscape LINUX MAC WIN
Sketchup