How can I reimburse the doctor after paying social security? Is the money in the medical insurance card useful if it is not used all the time?

Social security cards are actually paid in two parts, one is paid by the company, and the other is paid by yourself.

Medical part: your own money can be saved, even if you don't use it all the time, it will still be there. This part is relatively small, and the company's money cannot be saved. As long as you pay it every month and don't stay in hospital, the money will be gone. If you are hospitalized, social security will reimburse you. It means that all of us pay social security, and the social security bureau gives all the money to those in need. Equivalent to risk transfer

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