Yom Kippur 2014 begins at sunset on Friday, October 3 and lasts through Saturday, October 4.

Yom Kippur (Hebrew: יוֹם כִּפּוּר, IPA: [ˈjom kiˈpuʁ], or יום הכיפורים), also known as Day of Atonement.

The following article is quoted from: http://www.chabad.org/holidays/JewishNewYear/template_cdo/aid/177886/jewish/What-is-Yom-Kippur.htm

“Yom Kippur is the holiest day of the year—the day on which we are closest to G‑d and to the quintessence of our own souls. It is the Day of Atonement—“For on this day He will forgive you, to purify you, that you be cleansed from all your sins before G‑d” (Leviticus 16:30).

For nearly twenty-six hours—from several minutes before sunset on 9 Tishrei to after nightfall on 10 Tishrei—we “afflict our souls”…

Before Yom Kippur we perform the Kaparot atonement service; we request and receive honey cake, in acknowledgement that we are all recipients in G‑d’s world, and in prayerful hope for a sweet and abundant year; eat a festive meal; immerse in a mikvah; and give extra charity. In the late afternoon we eat the pre-fast meal, following which we bless our children, light a memorial candle as well as the holiday candles, and go to the synagogue for the Kol Nidrei service.

In the course of Yom Kippur we hold five prayer services: …

The day is the most solemn of the year, yet an undertone of joy suffuses it: a joy that revels in the spirituality of the day and expresses the confidence that G‑d will accept our repentance, forgive our sins, and seal our verdict for a year of life, health and happiness. The closing Neilah service climaxes in the resounding cries of “Hear O Israel . . . G‑d is one.” Then joy erupts in song and dance (a Chabad custom is to sing the lively “Napoleon’s March”), followed by a single blast of the shofar, followed by the proclamation, “Next year in Jerusalem.” We then partake of a festive after-fast meal, making the evening after Yom Kippur a yom tov (festival) in its own right.”

The following is mostly quoted from Wikipedia:

Yom means “day” in Hebrew and Kippur comes from a root that means “to atone”. Thus Yom Kippur has come to mean “day of atonement”. Some say there is a link to kapporet, the “mercy seat” or covering of the Ark of the Covenant. Abraham Ibn Ezra states that the word indicates the task and not just the shape of the ark cover; since the blood of the Yom Kippur sacrifice was sprinkled in its direction, it was the symbol of propitiation.

Universally observed

As one of the most culturally significant Jewish holidays, Yom Kippur is observed by many secular Jews who may not observe other holidays…

General observances

Leviticus 16:29 mandates establishment of this holy day on the 10th day of the 7th month as the day of atonement for sins. It calls it the Sabbath of Sabbaths and a day upon which one must afflict one’s soul.

Leviticus 23:27 decrees that Yom Kippur is a strict day of rest.

The traditions are as follows:

1. No eating and drinking
2. No wearing of leather shoes
3. No bathing or washing
4. No anointing oneself with perfumes or lotions
5. No marital relations

In order to apologize to God, one must:

1. Pray
2. Repent
3. Give to charity

A break-fast is the meal eaten after Jewish fast days such as Yom Kippur and Tisha B’Av.

At the end of Yom Kippur, Jews traditionally share a joyful Break Fast meal with family and friends. The Yom Kippur Break Fast is generally a festive breakfast menu consisting of foods such as eggs, cheese, bread. Here is a recipe for egg soufflé.

http://kosherfood.about.com/od/dairymaindishes/r/egg_souffle.htm