You can find info on numerous sites. Here is a snippit from the History Channel:
Ancient Origins of Halloween
Halloween’s origins date back to the ancient Celtic festival of Samhain (pronounced sow-in). The Celts, who lived 2,000 years ago, mostly in the area that is now Ireland, the United Kingdom and northern France, celebrated their new year on November 1.
This day marked the end of summer and the harvest and the beginning of the dark, cold winter, a time of year that was often associated with human death. Celts believed that on the night before the new year, the boundary between the worlds of the living and the dead became blurred. On the night of October 31 they celebrated Samhain, when it was believed that the ghosts of the dead returned to earth.
It has evolved over the years and demons are mostly forgotten, exchanged for a gluttony of sugar.
We teach our children how to go door to door and beg. And if not satisfied, they can vandalize.
Yeah, I don't see the hype about it. Just one more commercially driven reason to spend money. I fear that I am becoming one of those older cranky people who complain about people having a good time.... I just don't get this holiday (or the modern twist on most holiday celebrations)