Shintoism does not have one main god. It has over 8 million different kamis (spiritual beings that exist in animals, plants, nature, etc). A large majority of Japanese people worship Amaterasu as the "main" kami of Shintoism. Amaterasu is the goddess of the sun.
Shintoism is a religion located in Japan and related to Buddhism. Shintoism focuses particularly on nature and ancestor worship. Source: Human Geography: People, Place and Culture Eighth Edition H.J. De Blij, Alexander B. Murphy, and Erin H. Fouberg
It depends on how you count it. Most Japanese (roughly 80% of the 135 million population -- 108 million) are Shintoists in name, but rarely pray and only visit a Shinto Shrine once or twice a year (usually for New Year festivals).
Shintoism is indigenous to Japan as a spiritual practice of their people. As such, they would not normally read the Judeo-Christian Bible. However, this does not mean someone who practices Shintoism could not or has not read the Bible.