First, explore some of the hundreds of tribes (nations) in North America.
Northeast Tribes
Southeast Tribes
Great Plains Tribes
Southwest Tribes
Arctic, West, and Northwest Tribes
Caribbean
Next, make your decision, and then research that one tribe/nation
Using the US History Database, search for the name of the tribe/nation you chose. Focus in on the reference sources, especially the UXL Encyclopedia of Native American Tribes and the Gale Encyclopedia of Multicultural America.
For more information on a specific tribe:
http://www.nativeculturelinks.com/nations.html