[Leica] Question about photography business

[Brian Reid]

I've been taking pictures for money (mostly weddings and portraits) for 
40 years. I've always had a day job; I'm not good enough to try to make 
a living at it. The money I make has paid for lenses and printers but 
has never paid the mortgage or bought food.

Recent circumstances require that I become a registered business. 
Obviously it would be a sole proprietorship. I know lots about cameras 
and computers but nothing about business licensing.

Does anybody have any suggestions as to where I should start, to make my 
little "Brian Reid Photography" venture be a registered business? Since 
I live in California I assume that I would register in California, but I 
am baffled by what I find with search engines.