There seems to be some confusion over what constitutes the Catholic Church. Because of that, I thought I’d offer this look at the Church, its structure and hierarchy.
The Catholic Church is composed of 22 (or 23) *sui iuris *(Latin for “in their own right”) Churches. Each of these Churches is an independent Church that is in communion with Rome. By virtue of being in communion with Rome the Pope has authority over the Churches, although this is usually exercised through the leadership of the Churches.
The Roman Catholic (or, more accurately, the Latin Rite Catholic) Church is far and away the largest with over 1 billion members. The head of the Roman Catholic Church is the Bishop of Rome who, because he is the Bishop of Rome is also the Patriarch of the West and the Pope. Ranking below a patriarch are the Cardinals of the Catholic Church. This is an honorary title give to certain bishops. It may be because they are the head of a Curial Congregation (Cardinal Deacon), head a major diocese (Cardinal Priest), or are the pastor of one of the six major churches in rome (Cardinal Bishop). Archbishops are the head of major dioceses (Archdiocese) and bishops are the heads of dioceses. All bishops have a diocese for which they are responsible. Auxiliary bishops have a “titular diocese” – that is, a diocese that no longer exists. This is in keeping with the old tradition of "one city, one bishop). Working with the bishops are priests and deacons.
The primary form of worship for Roman Catholics is the Mass which may also be called the Liturgy.
The **Eastern Catholic **Churches comprise the remainder of the Catholic Church. They may be headed by a Patriarch (Armenian, Chaldean, Coptic, Maronite, Melkite and Syriac Churches), a Major Archbishop (Syro-Malabar and Ukrainian Churches), or Episcopal Churches (Bulgarian, Albanian, Croatian, Greek, Hungarian, Italo-Albanian, Ruthenian and Slovakian Churches). There are also Eastern Catholic Churches with no hierarchy of their own (Byelorussian, Georgian and Russian). These function directly under the authority of the local Roman Catholic bishop (although, in Los Angeles, the Russian Catholic Church, while technically under Cardinal Roger Mahony, functions under the auspices of the Melkite Eparch, Abp. Cyril).
Eastern Catholic Churches generally came into communion with Rome from an Orthodox Church. The exceptions are the Maronite and Italo-Albanian Churches which have no Orthodox counterpart. Following the dictates of Vatican II, these Churches retain what is authentic to their tradition including worship, vestments, theology and disciplines (for example, Eastern Catholic priests may, in general, be married provided they were married before they were ordained to the diaconate). Bishops are always drawn from celibate clergy, and usually from the ranks of the monastics.
Eastern Catholics are just as Catholic as Roman Catholics. Because of the nature of the relationship with Rome, any Catholic (whether Latin or Eastern) may partake of the sacraments/mysteries at any Catholic church, whether Eastern or Roman.