Jewish holidays start at sunset the night before and end at nightfall the last day. This goes back to the creation story in Genesis. Where the Torah says "There was evening and there was morning..." Since evening came first, our "days" start the evening before. So for Shabbat, it begins Friday evening, 18 minutes before sunset. That is when we light candles. Shabbat ends at nightfall on Saturday. Nightfall is when you can see 3 stars in the sky.
Last night was the beginning of Yom HaShoah. Yom HaShoah is known as Holocaust Remembrance Day. It is the day we remember the 6 million who were killed during the Holocaust by nazi Germany. It was started in 1953 when the Prime Minister of Israel (David Ben-Gurion) and the President (Yitzhak Ben-Zvi) signed it into law as a national memorial day.
Many Jewish households (including ours) light a special yellow candle to remember all those who lost their lives.
To learn more about the Holocaust you can visit the United States Holocaust Memorial Museum
Click on "History" on the top bar to read about the history of the holocaust.