There are several options for transmitting/interpreting the gcode and controlling the stepper motors. The cheapest (but still quick and easy) way is to use pololu stepper motor controllers with an arduino board. This is sufficient for the smaller stepper motors (under 2A).
Some kind individuals have written grbl, https://github.com/grbl/grbl You can just use the Arduino IDE iterface to upload the code to the arduino. Then you'll want to use the universal gcode sender https://github.com/winder/Universal-G-Code-Sender to upload your gcode to the arduino. It all works great.
You are a little limited with the interface. If you want more control I would suggest moving to an actual CNC controller and Mach3. Of course this will cost more.