The Jewish day begins and ends at sundown. Thus, all holidays begin at sundown of the day preceding the date shown and end at sundown of the (last) day shown.

Since the Jewish calendar begins with Rosh Hashanah, the Jewish year always straddles two years from the civil calendar. In other words, spring holidays (such as Pesach and Shavuot) occur in the civil year following Rosh Hashanah.

An additional note: not all Jews observe two days for holidays shown as lasting two days.

SHABBAT- The Sabbath; every week from Friday Evening to Saturday evening; one of the holiest days in the calendar. every Fri-Sat
ROSH HASHANAH - The Jewish New Year; start of the Ten Days of Penitence.
YOM KIPPUR - Day of Atonement; a very solemn day of the year, devoted to fasting, prayer, and repentance.
SUKKOT- First two days of Tabernacles; commorating the dwelling of the Israelites in booths in the wilderness.
SHEMINI ATZERET- Eighth Day of Assembly and SIMCHAT TORAH - Rejoicing of the Law.
HANUKKAH - Festival of Lights; victory of the Maccabees and rededication of the Temple.
PURIM - Celebrates defeat of plot to destroy the Jews of Persia.
PESACH - Passover; deliverance of the Jewish people from Egypt. The Seder service on the first two evenings recounts the story of the Exodus.
The last two days of PESACH are also observed as full holy days.
SHAVUOT - Feast of Weeks; marks the giving of the Law (Torah) at Mt. Sinai.