Counting the Omer Seven weeks from Passover, the 15th of Nisan (late March or April), until Shavuot, 6th day of Sivan (late May or early June)
Passover/Pesach (7-8 days) - Commemorates the deliverance of Israel from slavery in Egypt, celebrates freedom from oppression. [Observed with dietary restrictions, the Seder meal (representing their hardships), and recitation of the Haggadah (relating the Exodus).]
Shavuot/Feast of First Fruits - Festival of thanksgiving for the first fruits of the grain harvest. Also commemorates Moses' receipt of the Ten Commandments/Israel's acceptance of the Law (Torah).
Summer: Judgement/Exile
Days in the Midst of Distress Three weeks of sorrow, from 17th day of Tammuz (after summer solstice) to 9th day of Av (late July)
Shiv'ah Asar b'Tammuz - Fast day commemorating the smashing of the Torah tablets by Moses and the breach of the walls of Jerusalem before the destruction of the Second Temple
Tish'a B'Av - Fast day mourning the destruction of the first and second Temples and commemorating the beginning of exile.
Fall: Repentance
Days of Awe and Repentance 10 days, starting the 1st day of Tishrei (Sept or early Oct)
leading directly into Sukkot, starting the 15th day of Tishrei
Rosh Hashanah - Commemorates creation of the World; begins 10 days of penitence for harm done.
Yom Kippur/Day of Atonement - Day of fasting, making reparation for harm done, and helping those in need.
Sukkot (7-8 days) - Feast of Ingathering/Feast of Tabernacles - Festival of thanksgiving for the fruit harvest; originally. Also commemorates the years in the wilderness after leaving Egypt.
Winter: Joy/Victory
Starting with Hanukkah (late Nov or Dec) and ending with Purim. Purim is always one month before Passover/Pesach, which leads us back to the beginning.
Hanukkah/Festival of Lights (8 days, starting on the 25th day of Kislev) - Commemorates the struggle for religious freedom and re-dedication of the Temple. Menorah candles are lit. [Also commemorates the end of the olive harvest and the Winter Solstice.]
Tu B’Shevat/New Year for the Trees (15th day of Shevat) - Celebrated with tree plantings and orchard blessings. Seeds are planted for the bitter herbs for Passover/Pesach.
Purim/Feast of Lots (14th day of Adar) - Celebrates a major victory over oppression and is recounted in the Megillah, the scroll of the story of Esther. Queen Esther defeats a plan to massacre all the Jews in Persia. Purim takes place on the fourteenth and fifteenth days of Adar, the twelfth month of the Jewish calendar.