Glad it helped Anthony. Since then I've thought of a couple more things.
First, the reason Dawai's system seems complicated in description is because he is building some of the basic components I listed from scratch. Essentially he's building a replacement for the computer, in fact.
You don't have to do that. you can just go with pre-built black boxes and a regular older computer. In his system one of the main building blocks uses a microprocessor which also needs control programming. It's very cool, and interesting to hardware hackers (me included), but again, not something you would have to do at all.
As far as operating your machine, G-code shouldn't be frightening. It is actually very simple, but yes usually a program writes the G-code for you nowadays. Usually it is CAM software which translates what you draw in CAD to the G-code needed to do the work by the machine.
Just briefly, G-code is a simple list of commands, like "move to point x,y z". On your mill, without CNC, you would do the same thing by cranking handles to get to a position you want to plunge in at.
That's all it is. simple list of mechanical instructions. It may then say "move to Z - 3.000" That would mean lower the mill head 3mm (and presumably start cutting).
Say you wanted to move to x=1, Y=2 and Z=4. And then plunge into the material to Z= -3. Here's what the actual G-code for those two instructions might look like:
G00 X1.000 Y2.000 Z4.000
G01 Z-3.000
G00 means "move as fast as you can to this position"
G01 means "move at the feed rate to this position"
X, Y and Z just tell what axis to move
The feed rate was set earlier in your program by a different G-code -- not shown. You can change it at any time.
That's the basics. Obviously there are a LOT of available G-codes. Some for cutting circles, or peck drilling, or tapping, or changing tools, or changing feed rates or changing from metric to imperial units, etc, etc. But all undertandable if you just look at it this way -- it's just a list of commands. Of all the kinds of things you want to do.
Sometimes I think the easiest way to learn it is NOT to try to follow a course of study, but just to have your CAM program generate a simple G-code program for a simple part, and just read through the program, and look up the G-codes as you go along. Just as if you were the mill and you needed to know what way to move. You will quickly pick up the basics and probably have some of the most common G-codes memorized in a day. And that's probably all you'll need for quite some time -- the rest you'll pick up along the way. Don't let giant dictionaries of G-codes snow you -- you don't need to know every command and a lot of the jargon for an exam. You just want to learn how to use your machine for practical personal uses -- the rest will follow.
PS, if you want a simple free CAD program linked with a simple free CAM G-code output capability, try SketchUp with Sketch-U-Cam installed.
Best to first go to the Sketchucam website,
http://sketchucam.jimdo.com/ before getting Sketchup from Trimble -- that way you will have enough info to know what you want and how to install and configure it.