Halloween is celebrated in many countries on the night of October 31st. Children wearing costumes go to peoples' homes saying "Trick or treat!" to ask for candy and sweets. This practice originally involved a trick. A trick means someone will do something bad if they do not get a treat. In simpler terms it could be explained as: "Give me a treat or I will play a trick on you." Today however, people usually do not play tricks if they do not get treats. However, some people still get up to mischief by playing pranks or doing things to make fun of people; like putting toilet paper in trees; writing on windows with soap or throwing eggs at peoples' houses. People sometimes dress up as ghosts, witches, goblins and other scary things for Halloween
The Pagan holiday Samhain, that the All Saints day replaced, was also known as the Day of the Dead. Many Wiccans and modern Pagans celebrate the Day of the Dead, even today. This is considered a happy holiday, even though it celebrates 'death'. It is the day that the souls of dead people are believed to come back to Earth and walk among their relatives and friends; sort o a one day family reunion each year.
I hope this gives you a good idea as to what Halloween is about.
~Samantha :)