What is Yom Kippur
What: Yom Kippur is the holiest day of the year, when we are closest to G‑d and to the essence of our souls. Yom Kippur means “Day of Atonement,” as the verse states, “For on this this day He will forgive you, to purify you, that you be cleansed from all your sins before G‑d.
How: For nearly 26 hours we “afflict our souls”: we abstain from food and drink, do not wash or apply lotions or creams, do not wear leather footwear, and abstain from marital relations. Instead, we spend the day in synagogue, praying for forgiveness. (Chabad)