what are the parts of electric arc welding machine?

There are several types of arc welding machines.
1. The machine that we find in most shops. This is a somewhat stationary machine that has 1 Main cable that receives energy from the source (Usually 3 phase 220 or 440 Volts AC), the starter or switch, the transformer, the rectifiers, the controls of tension (Voltage) and current (Amps-or-Amperage), the two secondary wires: one is to ground the machine to the building + structure + part that you are to weld, the other is to put your electrode and produce the welding. Some other Arc welders are known as "wire welders" these use a reel of wire that will be the metal you provide in the welding, and instead of the solid flux that you have in the electrodes, you will use a gas that helps the welding to happen, the metal to melt and deposit. Wire welders have a metal reinforced hose that travels along with the secondary cable to the tip of the gun. The wire is pushed by an electric motor that is triggered at the gun, this wire travels through through the hose, which also allows the gas to flow as well.
Other type of welder which is usually portable, may work with a generator normally operated by a gasoline engine. These do not require rectifiers since the generator is providing already Direct Current (DC). Same thing, the secondary may use electrodes to weld or a wire gun. These wire welders are more common nowadays. Only specialized welding like non ferrous metals are still popular in form of electrodes.