Wow!
I was surprised that not a single person mentioned you do not HAVE to be a corporation (or S Corp, or LLC, or any other 'structured' business entity)!
You can always go into business for yourself, by yourself, as a sole-proprietor. When you are still small scale, and especially if you have no assets to start with, this can be an especially attractive option.
For one, it's easier to file taxes... only a Schedule C on your 1040 long form, instead of a a whole new set of forms. You also can get an EIN from the IRS as just a sole proprietor. This legitimizes your business, and helps prove that you are actually intend to be 'in business.'
Of course, if you have partners, just form a partnership. But there are two kinds, and this is where the big decision lies, whether you have partners or not.... How much risk are you willing to take?
A General Partnership, like a Sole Proprietorship, puts all of the owners 'at risk'. This means is the business becomes liable for a debt, whether back taxes, employment fines, or you get sued for doing a bad job, or causing injury, if the business can not pay for it, then a claim for damages or repayment can be made against the owners.
By the way, the other kind of Partnership is a Limited Partnership, which protects only some, and not all of the Partners from risk. Plus Limited Partners can't be involved in the day-to-day operations of the business, so I wont dicuss that any further.
If you form a corporation, S Corp, LLC, etc.... the owners protect themselves from liability. They can not be held responsible for anything more than what they have put into it. If the business goes bankrupt, thats all she wrote. Unless criminal liability can be proven, the owners dont have to pay up for business damages. But the downside to Sole Proprietorships and Partnerships is that if the business still has debt after they go bankrupt or out of business, then the owners can be sued as well.
But then again, most states require a substantially different tax structure if you establish a business entity that protects you from liability. Thats fine if you have the legal and accounting knowledge to handle it. If not, you will incur many more costs than a start-up business may be able to afford, especially without operating capital. But if you don't, and are just getting off the ground, then you would bes best to consider a less structured entity.
The best bit of advice I could give, is to go to the US Small Business Administration Onlince center at
http://www.sbaonline.sba.gov/, and use the state links there to get comprehensive information about your options on a state-by-state basis.
But if you have any questions about California, I may be able to help. I have started a General Partnership and a Corporation up in California in the past ten years, and do know something about the process and requirements for this state.
Elohir