eloid,
1.Check out your local community college and see if they offer a course.
2.If you open Mach mill they have a description of all the g and m codes.
3.Use the wizards to do simple things and then follow the code line by line as it's highlighted in the display window.
Then try and write some code yourself and see how it goes.
4.You can scan the internet and may find some basic tutorials which will help you.
5.CNC Programing Techniques by Peter Smid ( covers a lot and you'll need discipline to stay at it ).
6.There is a program in mach called Teach, never used it, but you may want to have a look.
Have Fun,
RICH