The three main types of CNC machining operations are turning, milling, and drilling.

Turning
Turning is a CNC machining operation in which a cutting tool is moved along the axis of the workpiece to create a cylindrical part. A machine tool that can perform turning operations is a lathe. Examples of parts that can be created using turning are screws, shafts, and pipes.

milling
Milling is a CNC machining operation in which a cutting tool is moved across the surface of a workpiece to create flat or complex shapes. Machine tools that can perform milling operations are milling machines and machining centers. Examples of parts that can be created using milling are gears, brackets, and frames.

drilling
Drilling is a CNC machining operation in which a cutting tool is moved vertically into a workpiece to create a hole. Machine tools capable of drilling include drills and machining centers. An example of a part that can be created using drilling is the hole for a fastener.

There are also specialized CNC machining operations such as grinding, sawing, drilling, etc. These operations are used to create a specific type of part or to complete the surface of a part.