Subsidiaries of S-Corp
I understand from your question that you are referring to setting up a parent-child relationship between the holding S-Corp and the companies owned by it (those can be other S-Corporations, also called Qualified Subchapter S Subsidiaries, or just single member LLCs).
Keep in mind that those will be separate entities, each with its own bank accounts and its own liability, however being owned by the parent entity they would be considered as disregarded entities from tax perspective. I would recommend you to consult a CPA who will be able to better explain how the taxation of such structure is managed, as well as what formes are required to be filed in order to establish it properly.
Other than those tax related formalities the entities would be formed the usual way with the Secretary of State (or other responsible authority, depending on the state).