Answer:
Hey there!
First, a little background of this story. This story was written a long, long time ago by Native Americans of the Iroquois Tribe. It was passed down generation by generation, until in the 1800's a Iroquois writer wrote about it. One thing the story wants to explain is why there is land on earth, and the origins of the land.
At the beginning of the story, "The world on the turtle's back," we are told that in the beginning, there was nothing, but there was a "Sky World." Here, lived gods, who were like normal people. However, when a woman falls to the "Normal World" she is saved by birds, and placed on the turtle's back. The story goes on to tell, that a muskrat brings her soil, which she used to build the land. That is why, the land formed.
Let me know if this helps :)