catholic church
The Catholic Church refers to the main Christian body of believers following the teachings of Jesus Christ.  The Catholic Church is made up of laity and clergy.  The clergy are ministers ordained through Apostolic succession (successive ordination of ministers since the time of the apostles).  The are three types of ordination:  Bishop, Priest, and Deacon.  The bishop is the 'local ordinary' of an area of the Church (e.g. Philadelphia).  The priests are the bishops aids in the church and the deacons assist the priests.  The Catholic Church is very vocal in it's opposition to contraception, abortion, non-marital sexual behavior and unbridaled consumerism.  It claims as it's source of revelation the Old and New Testaments and Sacred Tradition, guided through the interpretation of the magisterium.  Many false teachings have been promulgated in an attempt to destroy the Catholic Church.  Included in these are: the nature of the Crusades, the actions of Pope Pius XII during WWII, that Jesus had children and the Church is trying to cover it up, and many more.  To learn more about the Catholic Church seek out the Catechism of the Catholic Church or a number of other books widely available.

Catholic Church -- refers to an actually assembly of Catholics... the building in which Masses are held and the Eucharist is present.
I went to a Catholic Church last Sunday.  The Catholic Church spoke out against contraception last week.