This could be a challenging assignment because if there is a defining principal to describe Native American beliefs, it would probably be that there is no defining principal to describe Native American beliefs. Native American tribes practiced a range of different religions and they included, but were not limited to, polytheistic, pantheistic, monotheistic, henotheistic, animistic, and shamanistic religions. There were some shared elements among Native American belief systems, but many differences, as well. In addition, it can be very difficult to understand Native American beliefs at the time of contact with Europeans because of the tremendous losses in culture, including language and religious practices, that have occurred during that time. However, by focusing only on current practices or even current knowledge of historical practices, one has to acknowledge that any overview will be incomplete.
If you have to have an outline that broadly covers Native American beliefs, we think this is a good starting point.