The Holy Season of Lent extends from Ash Wednesday until the Vigil of Easter. Consult a Catholic calendar for specific dates each year. Lent is traditionally observed as a season of private and public prayer, spiritual reading, good works, and self discipline through fasting and abstinence.
Lenten weekdays are generally fasting days—unless the calendar indicates the (relatively infrequent) observance of a saint's feast, such as that of Saint Joseph, or the Annunciation of Our Lady. Fasting implies the taking of one full meal, and two smaller meals—collations, or "snacks" to use the modern term. Eating or drinking between meals should be avoided, although water does not break the fast. Likewise, unsweetened coffee or tea.
Ash Wednesday, all Fridays, the Ember Days, and the Vigil of Easter (until the end of the Vigil Mass) are days of abstinence from meat and poultry. They are also days of fasting.
Abstinence from personal enjoyments--e.g. candy, cigarettes, liquor, movies, television, etc.—is also recommended. By learning to control legitimate desires, one gains strength to deal with the illegitimate ones that eventually come along.
Nothing in the Lenten Observance is intended to harm the health of the observant Catholic. If you have any question as to how these practices apply in you own personal situation, please discuss it with your Confessor. Those below twenty-one or over fifty-nine are excused from the Lenten fast, but not from the requirement to abstain from meat on the appointed days.
Remember also, that Catholics are obliged to make a good Confession each year, and to receive Holy Communion at least once (!) during the Easter Season. In these United States, the season extends from the First Sunday of Lent until Trinity Sunday. Again, consult a Catholic calendar for specific dates each year.