The Catholic Church is made up of 23 sui iuris Churches all in communion with the Bishop of Rome (the Pope). The Latin Church is the largest particular Church in the Catholic Church and the most common rite used in the Latin Church is that of the Roman rite. The other 22 particular Churches that make up the Catholic Church are known as Eastern Catholic Churches. The largest Eastern Catholic Church is the Ukrainian Greek Catholic Church followed by the Syro-Malabar Catholic Church and the Maronite Catholic Church, all of which are in full communion with Rome. 14 out of the 22 Eastern Catholic Churches use the Byzantine rite and thus are considered to be Greek Catholic Churches. Since all Eastern Catholic Churches are in full communion with Rome, Latin (Roman) Catholics can partake of Eastern Catholics sacraments and participate in all Eastern Catholic Churches. Since we are all in full communion with each other, we all believe in the same thing, we just have different traditions, but there is no disagreement over doctrine. Eastern Catholics account for about 20,000,000 Catholics out of the 1,200,000,000 Catholics in the Catholic Church.
Down below is a link to a Melkite Greek Catholic Divine Liturgy, a Greek Catholic Church in full communion with the Pope: