Polytheism is the belief in multiple gods. All forms of Heathenry are polytheistic, including Norse Heathenry.
The Norse Deities themselves are very numerous. Some are very well-known, such as Odin, Freyja, Loki, and Thor, while others are very obscure. Much like the rest of Heathenry, the Norse pantheon was never centralized, so different gods experience different levels of popularity at different places and times. A Scandinavian town by the sea may frequently venerate Njord or Ægir, while a mountain village may do the same with Skadi and Ullr.
The decision to venerate deities at all is up to the individual. The ins and outs of working with, worshipping, and venerating deities are discussed on the veneration page.