CNC machines are computerized machines that are controlled by coded instructions to perform machining processes like cutting, drilling, and shaping. There are different types of CNC machines for various operations like lathes, mills, routers, lasers, and plasma cutting. CNC machines work by using G and M codes input through programming software to control tool movements and machine functions. The main advantages of CNC machines are high precision, repeatability, flexibility, and increased productivity compared to conventional machines. However, they also have higher initial costs and require skilled operators and maintenance.