An arc welder is a tool used to join metal pieces together by creating an electric arc between an electrode and the metal. This intense heat melts the metal, allowing it to fuse as it cools. Arc welding is commonly used in construction, manufacturing, and repair work due to its efficiency and strength. There are different types of arc welders, including MIG welders and TIG welders, each suited for specific tasks. Safety is crucial when using arc welders, as they produce bright light and intense heat, requiring protective gear like helmets and gloves to prevent injuries.