This introductory article from Chabad.org explains the history, customs and deep spiritual significance of Yom Kippur, the holiest day on the Jewish calendar. The article briefly outlines what to do (and not do!) before, during and after Yom Kippur, as well as the the structure of the prayer services. With internal links to relevant videos, how-to guides, and articles, this is a great resource for those looking for both a basic introduction and a more in-depth exploration of this day.