Other contributors have said "What is in Native art?" is the same question as "What does Native American art tell you?" If you believe that these are not asking the same thing and should be answered differently, click here
I would be happy to tell you a lot about Native American's, however your society has been trying to learn these same things for the last 500 years (without much sucess).
They told them for entertainment, but also as a way of passing down their history and mythology. People listened as children, learned the stories word for word and repeated them to new generations.
Native Americans created art for the same reason every other group in the world has:
religious and mystical purposes decoration because they liked the result because they had time on their hands...
Most would say that the purpose for it was to tell stories and/or legands known by the native americans, and some others would say because they wanted to express emselves,just as we do today!