A sacrament as an outward sign instituted by Christ to give grace. We recognize that the Sacraments have a visible and invisible reality, a reality open to all the human senses but grasped in its God-given depths with the eyes of faith. When parents hug their children, for example, the visible reality we see is the hug. The invisible reality the hug conveys is love. We cannot "see" the love the hug expresses, though sometimes we can see its nurturing effect in the child.
The visible reality we see in the Sacraments is their outward expression, the form they take, and the way in which they are administered and received. The invisible reality we cannot "see" is God's grace, his gracious initiative in redeeming us through the death and Resurrection of his Son. His initiative is called grace because it is the free and loving gift by which he offers people a share in his life, and shows us his favor and will for our salvation. Our response to the grace of God's initiative is itself a grace or gift from God by which we can imitate Christ in our daily lives.
The saving words and deeds of Jesus Christ are the foundation of what he would communicate in the Sacraments through the ministers of the Church. Guided by the Holy Spirit, the Church recognizes the existence of Seven Sacraments instituted by the Lord. (USCCB)
There are three classifications of sacraments:
Sacraments of Initiation: Baptism, Confirmation, and the Eucharist. These sacraments celebrate the designation of one’s life, identity, and direction, toward God. They also help one to understand the importance of the help of others who believe the same things about this relationship and help us maintain our relationship with God, and who also collaborate in responding to Christ’s call to build a merciful and just world.
Sacraments of Healing: Reconciliation and Anointing of the Sick. These sacraments remind us that we are frail and in need of God’s love to restore us to our fullest selves. They are sacraments of hope that God’s love will help us through our weakness and that our failures and shortcomings are not what defines us in God’s eyes. Ultimately, our healing brings us through a life-long journey of transformation toward the person we hope to become, and will help us to enjoy eternal closeness and peace with God.
Sacraments of Vocation and Service: Marriage and Holy Orders. These sacraments declare our commitment to bring God’s work into the world through relationship and service to others. They are designated as vocation because they specify the ways in which we will live our lives in response to our baptismal call.