Soldering is a skill that can be easily overlooked in the design world but is a useful skill to know especially in electrical work.  The practical uses of soldering in the theater can range from models of props to repairing or preparing different electrical or sound elements.  For example when working with sound equipment, occasionally a wire may come loose and need to be fixed.  With the knowledge of soldering this can be easy.  To start one must have the proper tools and equipment such as, a soldering iron, solder, something to solder, a workspace to solder on, safety glasses, a small vice grip (optional), and most important if you have never soldered before, supervision.  Without getting into too many details, the basic principle of soldering is to heat up the two items being soldered, for example two wires, with the soldering iron.  Once they are hot enough one should be able to touch the solder to the wires and it should melt right on.  The carefully let it cool and you should have a nicely soldered joint.  For circuit boards the concept is similar but the soldered objects change.  With a circuit board the wires go up through holes in the board and then the ends are soldered to the copper on the board around the hole.  This type of soldering is used in more advanced circuitry where saving space is needed.  Both types of soldering are an important skill to learn and I would encourage all, who do not know how, to learn.

For a detailed step by step this website is helpful.