The precepts of the Church are duties that the Catholic Church requires of all the faithful. Also called the commandments of the Church, they are binding under pain of mortal sin, but the point is not to punish. As the Catechism of the Catholic Church explains, the binding nature "is meant to guarantee to the faithful the indispensable minimum in the spirit of prayer and moral effort, in the growth of love of God and neighbor." If we follow these commands, we'll know that we're headed in the right direction spiritually.
You may see different lists of precepts, but this is the current list from the Catechism.
The first precept of the Church is "You shall attend Mass on Sundays and holy days of obligation and rest from servile labor." Often called the Sunday Duty or the Sunday Obligation, this is the way in which Christians fulfill the Third Commandment: "Remember, keep holy the Sabbath day." We participate in the Mass, and we refrain from any work that distracts us from a proper celebration of Christ's Resurrection.
The second precept of the Church is "You shall confess your sins at least once a year." Strictly speaking, we only need to take part in the Sacrament of Confession if we have committed a mortal sin, but the Church urges us to make frequent use of the sacrament and, at a minimum, to receive it once each year in preparation for fulfilling our Easter Duty.
The third precept of the Church is "You shall receive the sacrament of the Eucharist at least during the Easter season." Today, most Catholics receive the Eucharist at every Mass they attend, but it wasn't always so. Since the Sacrament of Holy Communion binds us to Christ and to our fellow Christians, the Church requires us to receive it at least once each year, sometime between Palm Sunday and Trinity Sunday (the Sunday after Pentecost Sunday).
The fourth precept of the Church is "You shall observe the days of fasting and abstinence established by the Church." Fasting and abstinence, along with prayer and almsgiving, are powerful tools in developing our spiritual life. Today, the Church requires Catholics to fast only on Ash Wednesday and Good Friday, and to abstain from meat on the Fridays during Lent. On all other Fridays of the year, we may perform some other penance in place of abstinence.
5. Supporting the Church
The fifth precept of the Church is "You shall help to provide for the needs of the Church." The Catechism notes that this "means that the faithful are obliged to assist with the material needs of the Church, each according to his own ability." In other words, we don't necessarily have to tithe (give ten percent of our income), if we can't afford it; but we should also be willing to give more if we can. Our support of the Church can also be through donations of our time, and the point of both is not simply to maintain the Church but to spread the Gospel and bring others into the Church, the Body of Christ.