Ash Wednesday and Good Friday are days of Fast and Abstinence from eating flesh meat. The Fridays of Lent are days of Abstinence only. By "Fasting" is meant that we eat one full meal and two lesser meals. Seniors over 60 and those who are ill are not obligated to the law of fast.
Ashes are placed on the foreheads of those who participate in the liturgy for Ash Wednesday, the beginning of Lent, as a sign of penitential character of the Lenten season. They are imposed with either of two formulas: "Turn from sin and be faithful to the gospel" Mk 1:15 or "Remember, man, you are dust and to dust you will return" Gn 3:19
In the Old Testament, to "gird on sackcloth" and "roll in ahses" (Jer 6:26) is an act symbolic of mourning, sorrow and repentance (Est 4:1,3, Jb 2:8 42:6, IS 58:5, Jer 6:26, 25:34, Ez 7:30, Dn 9:3, Jon 3:6, 1Mc 3:47)
In the New Testament, the phrase "sackcloth and ashes" appears in Jesus' reproach against the unrepetant towns of Chorazin and Bethsaida: "Woe to you, Chorazin? Woe to you, Bethsaida! for if the mighty works done in you had been done in Tyre and Sidon, they would have repented long ago in sackcloth and ashes (mt 11:21, Luke 10:13)