A plumbing fitter installs, maintains, and repairs piping systems for water, gas, and other fluids, using blueprints and various techniques like welding, soldering, and assembly. Key responsibilities include cutting, fitting, and joining pipes, testing systems for leaks, and ensuring all work complies with safety regulations and codes. They work in various environments, from residential and commercial buildings to industrial sites, and often handle a wide range of tasks from simple fixture replacement to complex industrial piping installations.