You'll have to choose a form of business organization. Typical choices are corporation (C or S), limited liability company, partnership, etc. Odds are that if you're looking for venture capital, a corporate structure is best since that is the structure that allows you to sell stock. But depending on your needs, one of the other forms might be better. Your lawyer and/or accountant can advise you on the best approach.
Additional Resources
Abe Cable and Steve Christensen of law firm Miller Nash presented an excellent program at OTBC on selecting a business entity. Abe is a securities attorney and Steve is a tax attorney and CPA, so between them they cover the most important (and some times contradictory) considerations to the discussion. You can view a video of their program on the OTBC website.