Candles are intended to burn continuously for 7 seven days. They are used as sort of a "doorbell" for your ancestors or whomever you are calling on. Candle colors are important.
Red- Love, passion, energy, lust, sex, courage
White- Peace, truth, purity, destruction of negative energy. Can also be used as a substitution when you can't find a specific color
Black- repelling negative energy from others, protection and absorption and destruction of negative energy
Green- Money, fertility, luck, abundance and success