Writing G code is not as hard as some make it seem. The first thing you need to accomplish is to input a program into the machine. This will have to be done with an RS 232 cable. You will need a computer(an older one that has the serial port to accommodate this) to transfer the program. The program itself can be written in "notepad", and the software to deliver it is "hyper terminal", both windows programs. The biggest obstacle is getting the program into the machine. The BOSS operating systems have a very small memory for programs, probably around 12K characters. So once you load a program and use it , it must be removed before another can be loaded.
Read up on the manual and get the connection figured out first, and we can go from there.