It is celebrated at a time of the year when trees become bare and days become shorter. In other words this is the day when the forces of cold and death return to earth. People used to believe that it was necessary to fight against these forces in order to survive the tough winter months ahead. 

They had bonfires, and they used apples and nuts to drive away the witches and spirits that haunted civilisation on this particular night. Nuts were used to predict with whom you were going to marry. You had to put two nuts into the fire side by side, then give them names. It was a good sign if they glowed and burned together, but if one or both burst, it meant bad luck. A couple could also place two nuts into the fire to see if they would have a long and happy life together. 

Apples were used to forsee luck and fortune. One would bow ones head into a bucket filled with water and some apples, and try to catch an apple, the bigger the better since a bigger apple would bring you greater fortune. 

However, not all people celebrate Halloween for the same reason. Some celebrate it as a day for remembering the dead and others by making merry and seeking guidance for the future.