I'll be honest with you. Yom Kippur is my least favorite Jewish holiday, because you can't eat! But, on the other hand, I understand why we fast: to slow down our biological rhythm during a day of meaningful self-searching and earnest communication with G-d. Plus, sometimes it's healthy to cleanse your body during a day of fasting!
Most people know that we fast on Yom Kippur. But, there are three customs that you may or may not know about: wearing white, wearing a tallit (religious shawl) for Kol Nidre, and avoiding leather. This is why we do these things:
Wearing white: Some say that we wear white on Yom Kippur to be like the angels. On this day, we yearn to be lighter, more clear, and transparent. Another interpretation is that we wear white on Yom Kippur because of the white garments in which we will be buried, making white a reminder of our mortality.
Avoiding leather: There is a custom on Yom Kippur of avoiding wearing anything made of leather, because leather requires the death of a living creature. For this reason, you will see some people wearing canvas shoes, or even rubber Crocs, instead of leather shoes.
Wearing tallit at night for Kol Nidre: Kol Nidre evening is one of the very few times in the Jewish year when a tallit is worn at night. Ordinarily a tallit is only worn when it is light out and we can see the fringes. One reason why we wear a tallit to Kol Nidre is that we sing the Thirteen Attributes. Another reason is that tallitot are frequently white, and when we wrap ourselves in white tallitot, we can see ourselves as being like the angels, garbed in white light (see "wearing white" above!)
If you are fasting on Yom Kippur, we hope you have a meaningful fast. May you and your loved ones be inscribed in the book of life!