Passover is the fourteenth day of the month Nissan and is celebrated in Jewish homes with a Seder. The Passover Seder is a celebration of the miraculous deliverance of the Jewish ancestors from their bondage in Egypt.
The Feast of Unleavened Bread begins on the fifteenth day of Nissan and lasts for seven days. During the Feast of Unleavened Bread no food with leaven is eaten.
The Feast of First Fruits is a celebration of the barley harvest which begins in the month of Nissan. It was required of the Israelites to bring the first sheaf of their harvest to the Temple as a wave offering. The Feast of First Fruits also begins the counting of the Omer leading up to Shavuot
Shavuot is to take place exactly seven Sabbaths and one day or fifty days total from Firstfruits. In Hebrew Shavuot means “weeks”. Shavuot is often called Pentecost which means “fifty” in Greek.
Yom Kippur literally means “Day Of Atonement” and is essentially your last chance to change the judgment that will come when the books are closed and to demonstrate your repentance and make amends with God.