What is Halloween? Is it worshipping demons? Is it spirits walking the earth?
The word "Halloween" is derived from a few things; All Saints Day (1st November), Eve of All Hallows (All Hallows Eve) or Hallow Even.
The celebration of Halloween was originally the New Years Eve of the Celts, the eve of Samhain or "Winter's Eve". It was generally believed that the dead or disembodied spirits of all those who had died throughout the preceding year would come back in search of living bodies to possess for the next year. It was believed to be their only hope for the afterlife. All who were alive of course didn't want to be possessed by these lost souls so on the night of October 31st, villagers would extinguish the fires in their homes to make them cold and inhospitable then dress up in ghoulish costumes and parade around the neighborhood making as much noise as possible to frighten away the spirits looking for a live body to possess. Food and drink (which I'd say accounted for the crazy actions of the villages, not the fear of being possessed) would be left out for these costume wielding villages.
In general the whole custom of Halloween was brought to America in the 1840's by the Irish immigrants who were fleeing the country's potato famine. The evil side of Halloween was pushed forward mainly by the church. The church maintained that the gods and goddesses and other spiritual beings of traditional religions were diabolical deceptions and manifestations of the devil. Therefore the customs associated with Halloween were always represented by the church as being evil - ghosts, human skeletons, symbols of the dead, Satan and other creatures such as witches.