When is a double boiler used....when you're cooking over an electric or gas stove eye or maybe an open fire of another type?
Yes, a double boiler has a bottom pan of water, then another pot (or even a metal coffee can swimming in the water) with the substance that you want to melt or cook. In cooking, a double boiler is used in cooking delicate cream sauces or melting chocolate--things you want to use a gentle heat for, so they don't scorch.)
Bee Curious, what is a good temperature at which to melt and dip?
I have never dipped beeswax candles, so I can't help you on this. I've only melted beeswax to use for batiking fabrics and that was quite a few years ago. (I used melted wax to put a design on fabric, then dyed the fabric. Then you iron the wax out of the fabric by ironing it between sheets of newspaper or paper towels. The paper absorbs the wax as the iron melts it.)
If you google "dipping beeswax candles" I'm sure you'll find info on how to do it. I'd say just get the wax to melt and not much hotter, and it should work.
Good luck.