What is a diocese
Diocese is a concept, which is related to the Catholic Church. This is where specific dioceses are spoken of. It is primarily a grouping of several parishes, which are located next to each other and should work together. A diocesan priest is also always appointed, who should be in charge of it all. There are also diocesan masses with meetings every month, although it depends on the specific dioceses. The diocesan priest must know, what is happening in the area, because only then can he pass this knowledge on, at the so-called diocesan conventions. Deanery is a lesser term than diocese. The deaneries are much smaller and are part of the diocese.
The whole structure is the same: there are deanery exits, where important matters for several parishes are discussed. Such a division is very important in the Church, because thanks to this you can, however, control the work of parish priests and curates in a given area. Such boards exist for people too – if they have any doubts, they can always write or consult it, who heads a deanery or a diocese. If that doesn't help, you can always go even higher and try to contact someone in addition. It is the same with the court system in Poland, so it's not surprising, that this is how the faithful were divided in the Church.