How does a CNC machine work?

A CNC machine is a computer controlled carving machine. It generally speaking reads G Code that instructs the machine how to move, what feedrate and spindle speed to use, which cutting tool should be in the spindle, etc. The cutter that the machine has in the spindle will carve through the material (generally metal) and create the intended shape. The material that has been removed is called "chips" and it will usually be recycled.