What is Ash Wednesday?
Ash Wednesday, a day of fasting, is the first day of Lent in Western Christianity. It occurs 46 days (40 fasting days, if the 6 Sundays, which are not days of fast, are excluded) before Easter and can fall as early as 4 February or as late as 10 March. Ash Wednesday is observed by many Western Christians, including Anglicans, Lutherans, Methodists, Presbyterians, and Roman Catholics.[note 1]
According to the canonical gospels of Matthew, Mark and Luke, Jesus Christ spent 40 days fasting in the desert, where he endured temptation by Satan. Lent originated as a mirroring of this, fasting 40 days as preparation for Easter. Every Sunday was seen as a commemoration of the Sunday of Christ's resurrection and so as a feast day on which fasting was inappropriate. Accordingly, Christians fasted from Monday to Saturday (6 days) during 6 weeks and from Wednesday to Saturday (4 days) in the preceding week, thus making up the number of 40 days.
Ash Wednesday derives its name from the practice of blessing ashes made from palm branches blessed on the previous year's Palm Sunday, and placing them on the heads of participants to the accompaniment of the words "Repent, and believe in the Gospel" or "Remember that you are dust, and to dust you shall return".
(Taken from Wikipedia)
If you want to check out the liturgy for this service for the Church of England click here