There are many factors, customs, and traditions to take into consideration when planning your wedding ceremony. These days it’s acceptable to individualize the ceremony in just about every way. (Care to say your vows on a rollercoaster? Go right ahead!)
A relatively recent addition to the ceremony is the lighting of a unity candle (started around 1970). The way it’s usually done is, a representative from each family (usually the mothers of the bride and groom) lights two taper candles at the beginning of the ceremony. Later after the formal vows, the bride and groom use the two taper candles to light the large unity candle together.
The popular explanation is that the taper candles are lit to symbolize the love and loyalty that each family has for the bride and groom. The newlyweds then use these two flames to light the unity candle, bringing the love of both families together in united love for the new couple.