If the Seder is to take place on a Friday night, then the candles must be lit before sunset. All other nights the candles should be lit when you start the Seder, and only from a flame that was lit before the Holiday started.
It is customary that the woman of the household light the candles, but any adult may do it. Take a lit match or candle in your hand, and just before lighting the candles, say the following blessings:
Blessed are You, Hashem our G-d, King of the universe, Who has made us holy through His commandments, and commanded us to light the (Sabbath and) Holiday light.
Blessed are You, Hashem our G-d, King of the Universe, Who has kept us alive, sustained us, and brought us to this season.
Light the candles. Do not blow out the match. Put it down in a safe place, and let it burn out by itself.
May it be Your will Hashem my G-d and G-d of my forefathers that You show favor to me (my husband, my son(s) and daughter(s), my father and mother), and all my relatives; that You grant us and all Israel a good and long life; that You remember us with a remembrance that will grant us good and blessings; that You consider us with a consideration that will grant us salvation and mercy; that You bless us with great blessings; that You make our homes complete; and that You cause Your Presence to dwell among us.
Make me worthy of the privilege and grant me the merit to raise children and grandchildren who are wise and understanding, who love Hashem, and fear Hashem; may they be people of truth, holy offspring, devoutly faithful to Hashem, and may they illuminate the world with Torah and good deeds and with every type of activity that serves the Creator.
Please, listen to my request at this favorable time, in the merit of our mothers Sarah, Rebecca, Rachel, and Leah. And illuminate our lights so that they never get extinguished. Shine your «Face» upon us with joy and we will be saved, Amen.