Read a book or watch some YouTube on welding, then practice, practice, practice.
Get some scrap sheet metal (or new if you have to) and lay down 10 beads on a flat plate just to get the feeling of the gun. Then work on different kinds of joints so you can figure out the settings as well as the methods.
You can't lay weld onto air, so holes need backing material. For tiny holes or gaps in thin metal you can hold a copper paddle behind it to prevent burn through.
