The ashes represent a number of things. They are a reminder that we are mortals and will die - 'Remember man that you were dust and to dust you shall return.' The ashes are also a symbol of penance....
Many times on the Tuesday before Ash Wednesday, but there is no liturgical norm.
The ashes come from the Palms which were given out on the previous Palm Sunday, gathered, burnt, Symbolism "ashes to...