The first step on the path to having a successful game studio is the formation of a legal entity. Of course, if you were producing all of the game assets yourself, or if everyone else who is contributing is willing to give you the rights to their work, then an individual could act as the legal entity that owns the assets. But the usual course of action here will be the formation of a company since ownership is basic to any business venture, including the game industry. If you want to be able to sell what you make you must concern yourself with ownership issues. Why? Quite simply, you can not sell what you do not own.
You can register your site yourself through your state's appropriate agency. Or there are web sites that will do it for you and also contain information about the formation of a company. The My Corporation. site has a wealth of information to assist you and will handle the formal registration process for a nominal charge. Not a bad way to go...