Sketch your sculpture. Visualize it from all angles. Troubleshoot in advance by knowing what you are doing ahead of time. Welding deals with hot and potential dangerous materials. Most welders train for years as journeyman before mastering the process.
Buy sheets, pipes, wire or other materials at your local hardware store. Collect scrap metal, found objects, and existing pieces. Prepare them for welding. Wash the metal if dirty. Cut pieces to fit your purpose and make sure they are fit for welding. Clean the two surfaces to be fused. A wire brush works well to remove rust from metal. Rusty or corroded metal may be impossible to weld.
Prepare your workstation. If arc welding, you will need a ground to attach to, which could be as simple as a metal table leg. Wear eye protection. Gas welding requires a heat retardant surface, proper knowledge of how to use the gases and flux.
Begin to weld. Tack the pieces together in two spots. This will prevent warping of the metal due to the heat. Place one at the beginning and one at the end of the weld. Fill it in by welding the seam. Drag the rod along the edges of the two pieces. This will create a bead, or thin weld line. When the rod has melted down to within an inch from the end, replace it with a new one, welding again where you left off. Practice welding to improve your skills.