When you have made a Poké Ball Disc, Iron Disc, or Aluminum Ingot, right-click the Anvil while holding the item in your hand to place it on the anvil. Then, by HOLDING the left-click while using a hammer, hit the disc. Each item that you put onto the Anvil has three stages of completion. They are visually represented by discs getting rounder and Aluminum Ingots getting flatter. Once they have been affected three times you right-click on the anvil and the finished product will pop off.