The law of abstinence obliges those 14 years of age and older not to eat meat.
The law of fast obliges all those from ages 18 through 59 to refrain from eating between meals and to limit their eating to one full meal and two lighter meals for the day.
Ash Wednesday and Good Friday are days of both fast and abstinence. In the United States, all Fridays of Lent are days of abstinence.
More on the Discipline of Lent
Lenten Exorcisms (Scrutinies)
Pictures from Confirmation