According to Canon Law 1247:
On Sundays and other holy days of obligation, the faithful are obliged to participate in the Mass. Moreover they are to abstain from those works and affairs which hinder the worship to be rendered to God, the joy proper to the Lord’s day, or the suitable relaxation of mind and body.
According to Canon Law 1246:
§1. Sunday, on which by apostolic tradition the paschal mystery is celebrated, must be observed in the universal Church as the primordial holy day of obligation. The following days must also be observed: the Nativity of our Lord Jesus Christ, the Epiphany, the Ascension, the Body and Blood of Christ, Holy Mary the Mother of God, her Immaculate Conception, her Assumption, Saint Joseph, Saint Peter and Saint Paul the Apostles, and All Saints.
§2. With the prior approval of the Apostolic See, however, the conference of bishops can suppress some of the holy days of obligation or transfer them to a Sunday.
So basically on top of Sundays, on the following days we should do our holy days obligation:
*]1 January: Solemnity of Mary, Mother of God
*]6 January: the Epiphany
*]19 March: Solemnity of St. Joseph, Husband of the Blessed Virgin Mary
*]Thursday of the sixth week of Easter: the Ascension
*]Thursday after Trinity Sunday: the Body and Blood of Christ
*]29 June: Solemnity of Saints Peter and Paul, Apostles
*]15 August: the Assumption of the Blessed Virgin Mary
*]1 November: All Saints
*]8 December: the Feast of the Immaculate Conception of the Blessed Virgin Mary
*]25 December: the Nativity of our Lord Jesus Christ (Christmas)
According to Canon Law:
1250 All Fridays throughout the year, and the time of Lent are penitential times throughout the entire Church.
1251 Fasting requirement is determined by each bishop conferences. Fasting is required on Ash Wednesday and Good Friday, and should be every Friday all year except when it falls on the above days of obligation.
1251 Who must fast? All between the age of 14 and 60, although all are encourage to observe values that point to repentance.
1253 To reinforce the autonomy of each bishop conference to come up with the most appropriate ways for their faithful to observe fasting and abstinence.
Fasting and abstinence has a connotation to reduction of one's meal or forgoing a certain type of food or ingredient (eg. meat, salt, etc). However, it should be noted that fasting and abstinence should have a spiritual focus and to follow What Jesus Would Do. In no way that we should see that big meals, meat, salt etc is part of the evil world therefore we must let go.
Example of acceptable fasting or abstinence:
*]No road rage for a week or a certain day.
*]No sex during lent
*]Charity and other social justice activity
*]No TV, internet, iPod, going to the movie, etc
*]Not buying cigarette during lent
*]No sweets, chocolate, coffee during lent and advent
Again, it is not to think all of the above are pure evil, but the focus it that we are sacrificing something that we really like and enjoy and give that time for your spiritual journey like reading the bible, reading last week's missalette, reading a good Catholic book, pray the rosary or other devotional prayers, etc.
Eucharistic Fast. The ancient way states that we must take nothing except water and medicine from midnight until we receive the Blessed Sacrament. According to Canon Law 919:
*]One who is to receive the Most Holy Eucharist is to abstain from any food or drink, with the exception only of water and medicine, for at least the period of one hour before Holy Communion.
*]A priest who celebrates the Most Holy Eucharist two or three times on the same day may take something before the second or third celebration even if the period of one hour does not intervene.
*]Those who are advanced in age or who suffer from any infirmity, as well as those who take care of them, can receive the Most Holy Eucharist even if they have taken something during the previous hour.
Whew.... hope it helps.