G-code is the most common language used by fabrication machines including 3D printers, CNC routers, and laser cutters. One way to familiarize your self with G-Code is through the open source software packages used for RepRap: Repetier Host and Printrun (pronterface). I’m currently using Repetier Host, which seems to have more extensive documentation at this point.
Both Repetier and Printrun interface with the converters Skeinforge and Slic3r, which convert STL model files into G-Code. Right now I’m using Slic3r, which also seems to have more documentation at this point.
You can use all of these programs without a connection to a fabrication machine. All you need is an STL file. Once you have that, you can download Repetier Host and start with these directions to load your STL into the software. Repetier Host will run Slic3r to convert it into G-Code.
In Repetier Host, your G-Code will look something like the code in this window’s right-hand panel:
To understand it better, take a look at these G-Code guides:
We can go through these commands in class. Have fun!