What exactly does the social security center do?

In short, the social security center can be regarded as an agency or institution of the Human Resources and Social Security Bureau, which is responsible for the specific handling of social insurance, while the social security-related policy formulation and management functions are carried out by the Human Resources and Social Security Bureau, and the social security center is the window of the Human Resources and Social Security Bureau.

Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.