Ficticious name filing from county office.
Business license from local city hall.
Resale license from state office if your gonna sell something.
About $150.00 in total fees and whala, you are a real business. That is the basics in California anyway.
It is usually pretty simple to start a business. Check with your local Small Business Administration. They always have free info on how to get started to be a legit business. I have done it several times in Cali and my record is 4 hours from first office to set up as a legit business with PO box, phone, bank account, and all licenses in place.