Ash Wednesday is a special day in the Christian religion that usually happens in February or March. On this day, people go to church and a special kind of ash (like the one you see when you burn paper) is put on their forehead in the shape of a cross. The ash comes from burnt palms from the previous year's Palm Sunday.
The cross on the forehead reminds people that they are imperfect and that they need to be sorry for the things they have done wrong. Christians believe that they are supposed to be kind and loving to others, just like Jesus showed how to do. The ash helps them remember to try to be better people.
After receiving ashes, people spend 40 days doing things to make them better and closer to God. Some people give up something they like, like candy or TV, while others do nice things for others, like giving money to charity or helping their neighbors. This period is called Lent and it ends with a celebration called Easter, which is when Christians believe that Jesus rose from the dead.