Soldering is one of the most useful techniques a metal smith can have. It is used both to create new pieces and to repair damaged jewelry. Your torch can also be used for annealing.
What a jeweler calls soldering, would be called welding in non-precious metals. The basic procedure calls for taking the two pieces of metal that are to be joined, and placing them together. The solder is usually the same metal, but an alloy with a lower melting temperature than the pieces it is intended to bond. When the metal is heated to a high enough temperature, the molecules expand leaving space between them. At this moment, the solder melts and flows into those spaces. When the metal cools, you have one solid piece.
When metal get worked, bent, stretched, hammered, etc., it gets progressively harder. This has advantages, such as strengthening the prongs that hold a gem. However, when fabricating a new piece it can make the metal difficult to work with and, at the extreme, you might even have a piece break.
Metal that has been work hardened, can again be made more malleable by annealing. This is a simple process. Flux the metal to…