The world was believed to have been formed out of a bird's egg exploding. The sky was believed to be the upper cover of the egg, alternately it was seen as a tent, which was supported by a column at the north pole, below the north star.

The movement of the stars was explained to be caused by the sky-dome's rotation around the North Star and itself. A great whirl was caused at the north pole by the rotation of column of sky. Through this whirl souls could go to the underground land of dead, Tuonela.

Earth was probably believed to be flat. At the edges of Earth was Lintukoto, "the home of the birds", a warm region in which birds lived during the winter. The Milky way was called Linnunrata, "the path of the birds", because the birds were believed to move along it to Lintukoto and back. The Milky Way is still called "Linnunrata" in Finnish.

Birds had also other significance. Birds brought a human's soul to him at the moment of birth, and took it away at the moment of death. In some areas, it was necessary to have a wooden bird-figure nearby to prevent the soul from escaping during sleep. This Sielulintu, "the soul-bird", protected the soul from being lost in the paths of dreams.

From Wikipedia on Finnish Mythology