This course is the place to begin. It will give you an overview of what being a business owner is like, and provides links to forms, filings, and information necessary to get started on your venture.
Here are some more sources of information on starting your business.
SBA's Business Guide
NH SBDC's Evaluating Your Business Idea fill-in pdf
The IRS.gov Small Business and Self-Employed Tax Center
In addition, NH SBDC offers one-on-one business advising to prospective and current business owners who have the intent to build their businesses. You can go to our locations page to find your region and fill out a Request for Services form.