The United States of America, commonly called the United States and colloquially known as America, is a federal republic consisting of fifty states and a federal district. The country is situated mostly in central North America, where its forty-eight contiguous states and Washington, D.C., the capital district, lie between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the south. The state of Alaska is situated in the northwest portion of the continent, with Canada to its east and Russia to its west across the Bering Strait. The state of Hawaii is an archipelago in the mid-Pacific. The country also possesses several territories in the Pacific and Caribbean. Wikipedia
Public Transportation in the U.S. is notoriously bad. Train travel is sometimes possible, including subway systems in a handful of major cities, but buses are usually the way to get around for shorter distances. Some budget airlines cover short hops at a price competitive with the buses, but for larger jaunts air travel is usually required.
Many travelers opt to buy a car, rideshare, or hitchhike around the country. Craigslist.org, rideshare boards, and Couchsurfing.org (via various rideshare and city groups) seem to be the current favorites for arranging rideshare between various cities.