Candles should be lit approximately 18 minutes before sundown. 18 is the numerical (gematria) value of the Hebrew word life.
Light the candles, then cover the eyes and recite the blessing Then uncover your eyes and look briefly at the flames remembering how God created light out of darkness.
When a festival coincides with the Sabbath, recite the festival blessing.
Blessed are you, Adonai our God, King of the universe, who sanctified us with His commandments, and has commanded us to kindle the light of the Sabbath.
Baruk atah Adonai, Eloheinu meleck haolam, asher kidushannu b'mitzvotav vitzivanue l'hadlik ner shel shabbat.
Some believe the candles stand for husband and wife. Others chooses to remember Gods creation of light from a world of darkness.
One candle will do if you only have one. The blessing is recited by a women when possible.
Since creating a fire on the Sabbath is forbidden by those who still follow the Torahs commandments concerning the Sabbath, great care should be taken to have the candles lit before the Sabbath begins.
It is permissible to use (or transfer from) a flame burning continuously such as a pilot light, gas or candle flame.(1)
1). Chabad of Peoria Jewish Art Calendar - 2006.