GRBL is the gcode interpreter and is free.
Compiling and burning GRBL on your Arduino would be a good start.
Once it is done you need a GUI (Graphical User Interface)
For GRBL there's a couple of good ones:
- bCnc: https://github.com/vlachoudis/bCNC/wiki
- USG: UGS
- Ciliipeppr: ChiliPeppr - Hardware Fiddle
Only problem is that I don't think GRBL support rotary axis without source code modification.