Based around the concept of the world tree, which is cut down by hero of the Kalevala
Vainamoinen, the Finnish world view and mythology was of a old, Shamanic tradition, fairly removed from what became the Norse Myth
cycle, and far older. I am sure that at one point, the peoples of Sweden
also shared the same mythos, but it seemed to have become usurped by the Germanic
mythos. In the Finnish mythology one finds that the world was at first but an ocean, with a water spirit who floated around in the waters, but she was impregnated by the All Father and became the water Goddess who birthed Vainamoinen, and in her labour created Finland
. Interestingly in reality Finland itself was raised from the water as the ice cap retreated after the last Ice Age
. Finland continues to rise today, returning to its natural hight after so long under the hundreds of thousands of tons of weight inflicted by the ice. Much of Finland still lies below sea level, thus the name of the "Land of Thousand Lakes."
Out of this newly formed land comes man, and the bearded one, Vainamoinen helps them to live. And when the world tree grew too large, and was stifling the life of man, it was Vainamoinen who cut it down, teaching the peoples of Finland how to create farm land out of the endless forests. From here on out, much of the "Kalevala" is just various stories and little to enlighten the reader of the religious and mythological beliefs of the peoples of Finland before Christianity. Also written down at the middle of the 19th century, it can't be fully relied on. However, many scholars think that the basic tendency of the Finnish peoples was towards a Shamanic system, much like other Northern peoples. Some think that the old Finnish system was very close to the Sami culture, which is/was a nature spirit worshiping religion. The spirit of the old culture was perverted to a point by the intrusion of Swedish settlers, but due to the fact that most of Finland was left alone, much of the practices survived. Indeed in many areas they survived until the time of Lonnrot.
Obviously the Finnish mythology has much more in common with the Russian's and the other Baltic countries, particularly Estonia. Some of the gods of Thunder, etc. carry over between the two, but I am unsure of how much similarity in that sense existed in Finland, as I have only read that in one book.
Much more study must be done for the Mythology in Finland, or translated to English, as I understand the Finnish Folk Archives are one of the best in Europe. Most of the body of Finnish folk poetry for example, exists only in Finnish, as no one has attempted a wide-scale translation of the material into English, making it difficult for non-Finnish readers of speakers to make a study of the mythology.