The seven sacraments—Baptism, Holy Communion, Reconciliation, Confirmation, Marriage, Holy Orders and the Anointing of the Sick—are the life of the Catholic Church. Each sacrament is an outward sign of an inward grace. In worship, we give to God that which we owe Him; in the sacraments, He gives us the graces necessary to live a truly spiritual life.
Baptism, Confirmation, and Eucharist are sacraments of Christian initiation. They ground the common vocation of all Christ's disciples, a vocation to holiness and to the mission of evangelizing the world. They confer the graces needed for the life according to the Spirit during this life as pilgrims on the march towards the homeland.
Holy Orders and Matrimony, are sacraments of service, directed towards the salvation of others; if they contribute as well to personal salvation, it is through service to others that they do so. They confer a particular mission in the Church and serve to build up the People of God. (Catechism of the Catholic Church #1533 and 1534)
The sacrament of Reconciliation (Confession) and Anointing of the Sick (Last Rites) are sacraments that bring healing and forgiveness to those who are in pain.
In summary, a sacrament is one of the means God has chosen to influence our life in the direction of his purpose for giving us life.