Worship in the Catholic Church is almost completely centered on the Communion. People who are faithful to this religion are expected to take communion every Sunday and on certain holidays during the year. Mass is held daily in most churches and is essential element of the service at marriages, funerals and other Catholic events. Catholics participate in Mass as a celebration of the Eucharist - A sacrament and the central act of worship in many Christian churches, which was instituted at the Last Supper and in which bread and wine are consecrated and consumed in remembrance of Jesus' death; Communion (American Heritage Dictionary). Catholics are encouraged to attend mass frequently as a way of acknowledging God and being forgiven for their sins.
The Mass is made up of several parts of which the longest and most important are what's called "liturgy of the Word" and the "Eucharistic liturgy", during which Holy Communion is distributed.
Although the structure of Mass is usually kept the same, many churches have a variation in the use of music, prayer and readings to make service appropriate for a given occasion.
The main difference between a Catholic mass and any other service is that if one happens to be a) non-catholic or b) have not been to confession - that is, been forgiven for your sins by a priest - you may not partake in Communion. Communion is the most important part of the Catholic mass, as it symbolizes receiving the body and blood of Jesus as represented by bread and wine. People who are not faithful to the Catholic religion are still welcome at the mass. Some religions, i.e., members of Orthodox Churches, the Assyrian Church of the East and the Polish National Catholic Church may attend mass, and may receive communion however they must...