The 8th of November is remembered as the day that Siddhartha Gautama, the historic Buddha, is said to have gain Enlightenment there by making him the first Buddha and bringing the foundations of the faith to light.
Siddhartha Gautama spent many years trying to find the answers to life, spending time studding with several different teachers. He was unsatisfied with any of his studies and one day decided to break his fast and sat beneath a tree. The tree has been said to be a pipal tree. He vowed he would not get up or eat till he found the answers he searched for. Eight days later he came to what is now known as the Four Noble Truths which according to the Buddhist Temple of Chicago are
1. All beings are subject to suffering. No one escapes… suffering is universal.
2. The cause of suffering is Ignorance. And Ignorance of oneself is the greatest Ignorance.
3. Ignorance, the cause of suffering, can be overcome, and
4. The way to overcome Ignorance is the Eightfold Path.
Some traditions recognize Siddhartha Gautama birthday as more important then Bodhi Day but others see this as the most important of the days.
I found one website that gives ideas how to recognize this day though I do not know how accurate it is, it is an interesting read.
Chicago Buddhist Temple: http://budtempchi.org/bodhiwriteup.html
How to celebrate: