What is the main form of Catholic religion?

Answer 1

Your question is not entirely clear. I assume you mean what is the dominant Rite (form of worship) within the Roman Catholic Church. The answer to that is the Latin Rite (or Western Rite), which, despite its name, does not mean conducting services in Latin but instead using the forms of the Mass and other ceremonies that have become established historically in Western Europe and have since spread worldwide.

There are a number of other Rites, much smaller in influence than the Latin Rite. For example, the Byzantine Rite, whose ceremonies are in Greek, is very similar to the services conducted in the Eastern Orthodox Church but is entirely Catholic and under the authority of the pope.