Are Welding uses an electrical power supply (either AC or DC) to create an electrical arc between the electrode and the material that is being welded in order to melt the material. The electrode can be either consumable (it melts along with the base material) or non-consumable (it does not melt). The length of the arc is directly related to the voltage of the power supply, where the heat is related to the current (Amps) of the power supply.
In arc welding, an inert or semi-inert gas is typically used to protect the welding area, commonly called a shielding gas. The polarity of the electrode can have a great effect on the weld depending on the type of welding being done. For example, using a consumable electrode with a negative charge will result in a shallower weld, while a positive electrode will result in a hotter and deeper weld.