Yom Kippur begins at sundown on October 7 in 2011. It changes days every year, so be sure to check for what days it falls on in your current year if you read this after 2011.
This web page gives good background of biblical and jewish traditions as well as wonderful explantions of why this is important to Christians as well. It’s always important that as we read the old covenant scriptures that we can see Jesus (Yeshua)
Yom Kippur – the day of atonement
The biblical Holiday website is a wonderful site for learning the basics, especially good for home schoolers.