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”
For nearly twenty-six hours—from several minutes before sunset on 9 Tishrei to after nightfall on 10 Tishrei—we “afflict our souls”: we abstain from food and drink, do not wash or anoint our bodies, do not wear leather footwear, and abstain from marital relations.
Before Yom Kippur we perform the Kaparot atonement service; we request and receive honey cake, in acknowledgment 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: Maariv, with its solemn Kol Nidrei service, on the eve of Yom Kippur; Shacharit—the morning prayer, which includes a reading from Leviticus followed by the Yizkor memorial service; Musaf, which includes a detailed account of the Yom Kippur Temple service; Minchah, which includes the reading of the Book of Jonah; and Neilah, the “closing of the gates” service at sunset. We say the Al Chet confession of sins eight times in the course of Yom Kippur, and recite Psalms every available moment.