How does Beijing's social security transfer from one company to another?

There are two situations. One is that two companies pay social security in the same area, which is relatively simple. It is necessary to stop employees in the original company and then enroll in another company. At the same time, employees need to leave their jobs in the original unit and go through the entry formalities in the new unit. Another situation is that two units are not in the same area, so it is necessary to handle employee resignation and social security transfer, and then handle social security registration in another unit, and then transfer social security.