One day, Hiawatha mourns the fact that the wisdom of his elders never gets to pass directly to the children who aren't born yet. He decides that his people need some system of symbols to pass knowledge from one generation to another. Basically, he wants to invent writing.
Hiawatha starts walking around and painting different symbols in different places, making up special symbols for all kinds of concepts and things.
But it's not enough to make up symbols. Hiawatha also needs to teach his people how to read these symbols. So he does that too.
Hiawatha thinks it's especially important for people to have things written on their graves to help people remember them.
Hiawatha writes down all of his people's songs so that they will be remembered.