BSH is set in the Battlestar Galactica Universe, which occurs 150,000 years ago in a distant star cluster far from Earth. The Twelve Colonies of Kobol are a collection of human colonized worlds situated in four nearby star systems. In many ways their society mimics our own but they have much greater technology especially when it comes to space travel, robotics, and Artificial Intelligence. This last advance, AI, led to a massive twelve year war when their creations, the Cylons, revolted. The human colonies were forced to unite under a single government to combat the threat.
The Re-imagined Series is considered the canon base for the BSG universe, Colonial society, technological advances, etc.
Caprica and Blood and Chrome are considered to be canon except for their contradictions to the re-imagined series.
The original 1978 and 1980 Galatica series may be used for some reference but are considered non-canon.