What Are CNC Machines?
Computer Numerical Control (CNC) machines are automated milling devices that make industrial components without direct human assistance. They use coded instructions that are sent to an internal computer, which allows factories to fabricate parts accurately and quickly. There are many different types of CNC machines, ranging from drills to plasma cutters, so they can be used to make a wide variety of parts. Though most are used industrially in manufacturing, there are also hobby versions of most of the machines that can be used in private homes.
Programming and Operation
The code used to program CNC units is generically called G-Code. It contains information about where parts of the machine should be positioned, and tells the machine exactly where to place a tool. Other instructions tell the machine additional details, like the speed a part should run at; how deep it should cut, burn, or punch; and the angle of an automated tool. Most modern industrial CNC machines are tied into a network of computers, and receive operating and tooling instructions via a software file.
source: wiseGEEK - clear answers for common questions