Final answer:
When Yom Tov and Shabbat coincide, Yom Tov candles are lit first followed by the recitation of blessings for the holiday and Shabbat, ensuring that lighting occurs before the commencement of these holy days.
Step-by-step explanation:
When Yom Tov and Shabbat coincide, there is a specific order for the lighting of candles and the recitation of blessings. The procedure typically begins with the lighting of the Yom Tov candles followed by the recitation of two blessings: one for the candle lighting (Baruch atah Adonai, Eloheinu Melech ha'olam, asher kid'shanu b'mitzvotav v'tzivanu l'hadlik ner shel Yom Tov) and one for the sanctification of the holiday itself (Baruch atah Adonai, Eloheinu Melech ha'olam, shehecheyanu v'kiyimanu v'higianu lazman hazeh).
Then, after nightfall, the blessing for the sanctification of Shabbat over a cup of wine is recited (Kiddush), including a mention of both the holiday and the Shabbat within the blessing. It is essential to note that the candles should be lit before the onset of the holiday or Shabbat, as lighting a fire is prohibited during these times according to traditional Jewish law.