What is your question exactly?
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Yes, the subject is quite vast:)
A beginner's course for CNC machines is available here:
http://goo.gl/LZnrxn
Is this what you are looking for?
Indeed, the subject is vast and moreover there are several languages/programming techniques.
As for the ISO or "G" code you can direct your search on Google by typing "iut" in your search, in Mechanical Engineering there is a part of the program that deals with this problem in an affordable way.
Some links with the functions and their names:
http://sti.ac-montpellier.fr/IMG/pdf/prod_program_t1_20_40_60.pdf
http://fr.scribd.com/doc/79959570/Cours-de-programmation-ISO