The Orthodox Church
Almost two thousand years ago, Jesus Christ, the Son of God, came to earth and founded the Church, through His Apostles and disciples, for the salvation of man. In the years which followed, the Apostles spread the Church and its teachings far; they founded many churches, all united in faith, worship, and the partaking of the Mysteries(or as they are called in the West, the Sacraments) of the Holy Church.
The churches founded by the Apostles themselves include the Patriarchates of Constantinople, Alexandria, Antioch, Jerusalem, and Rome. The Church of Constantinople was founded by St. Andrew, the Church of Alexandria by St. Mark, the Church of Antioch by St. Paul, the Church of Jerusalem by Sts. Peter and James, and the Church of Rome by Sts. Peter and Paul. Those founded in later years through the missionary activity of the first churches were the Churches of Sinai, Russia, Greece, Serbia, Bulgaria, Romania, and many others.
Each of these churches is independent in administration, but, with the exception of the Church of Rome, which finally separated from the others in the year 1054, all are united in faith, doctrine, Apostolic tradition, sacraments, liturgies, and services. Together they constitute and call themselves the Orthodox Church.
The teachings of the Church are derived from two sources: Holy Scripture, and Sacred Tradition, within which the Scriptures came to be, and within which they are interpreted. As written in the Gospel of St. John, “And there are also many other things which Jesus did, the which, if they should be written every one, I suppose that even the world could not contain the books that should be written” (John 21:20). Much teaching transmitted orally by the Apostles has come down to us in Sacred Tradition.
The word Orthodox literally means right teaching or right worship, being derived from two Greek words: orthos (right) and doxa(teaching or worship). As the false teachings and divisions multiplied in early Christian times, threatening to obscure the identity and purity of the Church, the term Orthodox quite logically came to be applied to it. The Orthodox Church carefully guards the truth against all error and schism, both to protect its flock and to glorify Christ whose body the Church is.
From the Orthodox Christian Information Centre -
http://www.orthodoxinfo.com/general/ with a direct link at