Ash Wednesday gets its name from the practice of placing ashes on the foreheads of the faithful as a sign of repentance. The ashes used are gathered after the Palm Crosses from the previous year's Palm Sunday are burned. In the liturgical practice of some churches, the ashes are mixed with the Oil of the Catechumens(one of the sacred oils used to anoint those about to be baptized), though some churches use ordinary oil. This paste is used by the priest who presides at the service to make the sign of the cross, first upon his own forehead and then on each of those present who kneel before him at the altar rail. As he does so, he recites the words: "Remember (O man) that you are dust, and to dust you shall return."
It is also the first day of Lent and is exactly 46 days from Easter Sunday 40 days if you miss out the Sundays.