Recommended reading: Guerrilla guide to CNC machining

Very good introduction to hobby CNC machining:

https://bonmotwang.wordpress.com/2011/03/03/guerrilla-guide-to-cnc-machining-and-resin-casting-part-1/

Strongly recommended..

Jakob E.

Good overview. The article doesn't mention though, that besides CAM there are newer programs, such as Intercon in Centroid, or Wizards in Mach3. With those one doesn't need to know G-code, or even CAD to program parts. Using series of preprogrammed basic shapes/lines/arcs/interpolations/drilling patterns one could learn how to make much more complicated parts just in an evening or two. 

Of course, to do it you need to know basics such as materials, use of appropriate tools, speeds, and feeds...

Best, M