You focus whatever energy you can into them, light them, and then you have to let them go.... let them burn out and disappear, you can't hold onto them. A candle isn't meant to sit there forever, no more than magic is meant to be held onto.
Large candles can work for prayers for guidance, growth, or other long term goals. Small candles that can be burnt out completely work best for short term goals and wishes. Using your athame or any knife ,you can carve words and symbols into your candles ,anointing them or loading them with herbs or powders for futher correspondance for your magick.
Green---Attracts money, wealth, and promotes herbal magic
Sea Green---Emotional healing, protection, calming
Yellow---Mental clarity, promotes concentration and knowledge, good for studying
Red---Lust, anger, hate, This is generally a bad color to use!!
Pink---New relationships, raises energy, promotes emotion and love
Rose---Self-love, enhancing of relationships of all types
Peach---Gentle strength and joy
Brown---Earth magic, protection,friendship.
Orange---This balances, nuetralizes, promotes prosperity and mental agility
Blue(general)---calming, Water Magick
Light Blue---Peace, patience, health, calming, relieves tension
Dark Blue---Promotes justice, banishes depression
Turquoise---Awareness, meditation, moon, creativity
Purple---Psychic enhancement, promotes change, expansion of desires, and strength
Lavendar---Intuition, dignity, spiritual shield, opening of the third eye
Black---Repels/banishes negativity, get rid of unwanted influences
Copper---Passion, the God, promotion of winning, safety and power of the male, happiness, playful humor
Gold---Represents the God, attration, persuasion
White---Hightens consciousness, protection, purity, represents the Goddess.
Silver---Purifies, protection, hieghtens awareness, promotes love, light and happiness
Grey---Nuetralizer to erase without reprecussion, illusion, depression