Sacraments are sacred rituals in the Catholic and Orthodox Churches. They are known as Mysteries in the Orthodox Churches.
Sacraments are efficacious signs, instituted by Christ to give grace. Simply put, the sacraments do what they represent. In other words, baptism not only symbolizes washing, it actually washes away sin.
There are seven sacraments in the Catholic Church: Baptism, Eucharist, Confirmation, Reconciliation, Marriage, Holy Orders, and Anointing of the Sick. In the Orthodox Churches, Confirmation is known as Chrismation. The Catholic Church sees in the Eucharist "the Source and Summit" of the faith.
You can find much written about the sacraments online. There are blogs dedicated to catechesis, apologetics, and evangelization. Other sites highlight the liturgical celebrations of the church calendar.