The seven sacraments are gifts from God. They are an encounter with God. It is an opportunity to receive God's grace. Baptism, Confirmation, and Eucharist (Communion) are called the "Sacraments of Initiation." Marriage and Holy Orders are "Sacraments of Service." Reconciliation (Confession) and Anointing of the Sick are "Sacraments of Healing." They are all special ways to meet God and grow closer to Him.
Some sacraments, like Eucharist, Marriage, Reconciliation, and Anointing the of Sick, can be received more than once. The others can only be received once.