This identification program is for birds in the northeastern and central parts of United States and adjacent Canada. Fill out the form as best as you can and you'll find which bird match. It's better to start with a few characteristics you are sure about, then add more as needed. Use the "Back" button to go back and add (or subtract) characteristics. If you want to see all the birds in the database, simply hit "Identify" without checking any boxes.
Some books that can help include:
Bird Characteristics: see this image (from Wikipedia) for a useful description of the terminology used below. For North vs. South, see this Google Map. North includes the northern half of Minnesota, Wisconsin, and Michigan, upstate New York, West Virginia and central Pennsylvania, and Vermont, New Hampshire, and Maine. All other states are South.