Staring a subsidiary company is the same as starting a new company. You have to set up the company's legal information, install the chart of account, and add the missing account depending on the country where the subsidiary started, set up the bank statement feed, and so on.
The most important configuration is to decide who will work under which company: not physically, but who will have access to both the companies. You have to prepare the list of users to allow them such access.
