There are literally hundreds of American Indian cultures and tribes in the United States. Each group has its own language, its own spirituality and belief systems, its own culture, music and ceremonies. There is no one way to describe them, no one way to understand them.
I personally do not like the term "Native American". You could easily say that anyone born in the United States is a "native" American. If there must be a generic term, I prefer American Indian or Aboriginal group.
I am sure that most people know about what was done to the Indian cultures by the European invaders, so I don't intend to go into a lot of detail here! The Indian is neither the vicious savage depicted in most history accounts and old movies, neither is the Indian the noble chief that many now envision. The Indian is a person, just like any other.
I do believe that we are still the invisible minority in this country. When you see a commercial on TV showing a group of different cultures, intended to express cultural diversity, how often do you see an Indian in the group? Are there any sitcoms on TV about an Indian family? Most movies that are made do not use American Indians in Indian roles.
We are victims of a U.S. apartheid system, not much different than that of South Africa for many years. Who else has to be "enrolled" with the government to "prove" their ancestry? Who else has to carry a card showing that they are descended from a particular culture?
Our spirituality has been stolen by the so-called "new agers", and the country is filled with fake "shamans", hucksters holding fake "ceremonies" and sweats for money, people making up "Indian" names and writing books... on the other hand, there are groups of Indians who attack any other Indian who is doing something that they do not agree with. It is a strange situation!
I have links here to sites that I like. You can learn a lot from them. All I ask is that you educate yourself.
http://www.hanksville.org/NAresources/ This site has links to a great deal of useful information
http://members.tripod.com/~PHILKON/ This site is all you will ever need. It is huge, and has links to every possible type of information that you could ever need. I am not kidding!
