Who can tell me the difference between "city" and "region"? The more detailed, the better.

The region is the agency of the province (or the government at the same level), while the city is the real first-level government agency, which is roughly the same from the level! However, the region is a nominal institution and a dispatched institution, so there are no people's congresses and CPPCC. And only the provincial people's congress working Committee and the CPPCC in a certain area are the same. The appointment and removal of judges and prosecutors in procuratorates and courts must go through the provincial people's congress. Therefore, the district is not really a first-level government, and it is sometimes called the administrative office.