The traditions of Ash Wednesday came up as a part of the Lenten customs during the late 5th century. Penitence and fasting are two of the key distinctives of Lent. Lent in the Western Churches was originally a period of forty days of fasting and penitence, readying the Christian soul for the great feast on the ensuing Easter Sunday. This is held as a period of sober reflection, self-examination, and spiritual redirection. The Lent begins on Ash Wednesday and goes for forty days excluding the Sundays. Because Sundays are always the joyful celebration of the Resurrection. It ends on the Good Friday. However, Lent is a forty two day period in Eastern Churches and begins on the Monday preceding the Easter by forty two days. This makes it clear that they don't have Ash Wednesday.
In time the emphasis of the season turned from preparation for baptism to more penitential aspects of penance. The sorrows and sufferings of Christ were shared by the self-denying Christian. Persons guilty of notorious sins spent the time performing public penances. Only at the end of Lent were they publicly reconciled with the Church. During the Middle Ages the sinners were accepted back in an elaborate ceremony.
Apart from getting ashed, the tradition is to pray, and go for fasting as a preparation for Lent. Wearing sack cloth and sprinkling the head with ashes was an ancient sign of repentance. The Biblical custom for repentance was to fast, wear sackcloth, sit in dust and ashes, and put dust and ashes on one's head. But the Bible does not specify the Ash Wednesday rites as such. In earlier ages a penitential procession often followed the rite of the distribution of the ashes, but this is not now prescribed.
Unlike the old days, we no longer normally wear sackcloth or sit in dust and ashes, the customs of fasting and putting ashes on one's forehead as a sign of mourning and penance have survived to this day. The Church has never chosen to make it or any other specific day the definitive commemoration of the concept of repentance. Still it is a deacon. Some churches observe it with distribution of ashes, reading prayers of repentance, and with other services offered from the pulpit.
This custom entered the church from Judaism. And is observed on Ash Wednesday, that marks the onset of a period of sober reflection, self-examination, and spiritual redirection. At first only public penitence received the ashes. They were made to appear barefooted at the church and perform penances for their sins. Friends and relatives began to accompany them, perhaps in sympathy and in the knowledge that no man is free from sin, and gradually the ashes were given to the whole congregation.
On this day all the faithful according to ancient custom are exhorted to approach the altar before the beginning of Mass, and there the priest, dipping his thumb into palm ashes previously blessed, marks the forehead of each the sign of the cross, saying the words: "Remember man that thou art dust and unto dust thou shalt return." In case of clerics it is upon the place of the tonsure. The saying and the act are meant for reminding us that man is mortal. This means we are dust and it is dust to which we shall return. The ashes used in this ceremony are made by burning the remains of the palms blessed on the Palm Sunday of the previous year. In the blessing of the ashes four prayers are used, all of them ancient. The ashes are sprinkled with holy water and fumigated with incense. The celebrant himself, be he bishop or cardinal, receives, either standing or seated, the ashes from some other priest, usually the highest in dignity of those present.