It is a mitswah to light candies on the eve of the Sabbath, before sunset, at home in the room where the meal is taken. The candies should be lit no later than eighteen minutes before sunset.
Customs vary as to the number of candies to be lit.
Upon lighting the candies the woman covers her eyes with her hands and recites the benediction asher kidshanu b'mitzvotav v'tzivanu l'hadlik ner shel shabbat . Covering the eyes is a gesture of prayer which helps in the attainment of Kawwanah , concentration. The reason for it here, however, is slightly more complicated. Normally a benediction is recited before the act is performed. This benediction marks the beginning of the Sabbath, and during the Sabbath we are forbidden to create light.