As I'm standing over the double-boiler, I stir in my dyes, scents, and herbs and will chant a phrase or a sigilized word that sums up my intention as I stir. It all feels so very bubble-bubble-toil-and-trouble. While chanting and stirring, I call up that mental scene again and will visualize it in the reflection of the molten wax, thus adding that psychic energy to my creation. As with anything in magic, the more energy and intention you put in, the more you'll get out.
Candles can often have things hidden in them to help create the desired effect. Stones, crystals, and non-flammable charms can be hidden in a candle by pouring a bit of wax for the bottom, waiting for it to cool enough to support the object, then adding the rest of the wax for the candle. I've seen people do multiple layers like this in taller candles where as each stone or charm was revealed, that were added to a mojo bag that was carried on the person.
As I let the candles cool and become solid, so does my intention, stored in the newly-created creature of wax. Once I am ready for that vision to manifest, I light the candle and activate the magic within. The burning flame transforms matter into energy and will into reality. Some candles I'll leave to burn until they burn out, and this is often done for spells that have a specific goal in mind - a candle to assist in a job search or one to bring closure to a situation. Others I use for more open-ended purposes. These I'll keep in the places I need them and burn as needed. My desk always has a few creativity-magic candles on it which I light as I am working on some creative endeavor, and I always have some purification candles in my bathroom that I light while doing a spiritual cleansing bath.
The burning of candles has enchanted humankind for thousands of years, and they continue to enchant my life through my work with them. The work of designing and building a candle with magical intent adds so much more personal power to my magic. I find hand-made candle magic to be one very satisfying way of practicing my Craft.