The tradition of Halloween was carried to America by the immigrating Europeans. Some of the traditions changed a little, though. For example, on Halloween in Europe some people would carry lanterns made from turnips. In America, pumpkins were more common. So people began putting candles inside them and using them as lanterns. That is why you see Jack o lanterns today.
Nicholas Rogers, a historian at York University says that when people prayed for the dead at Hallow Mass, they dressed up. When praying for fertile marriages, the boy choristers in the churches dressed up as virgins. So there was a certain degree of cross dressing in the actual ceremony of All Hallows Eve
More than a thousand years ago the Christian church named November 1 All Saints Day (also called All Hallows.) This was a special holy day to honor the saints and other people who died for their religion. The night before All Hallows was called Hallows Eve. Later the name was changed to Halloween.