Battlestar Galactica is a reimaginning of the 1978 series of the same name. In a future, the humans live in 12 colonies. The humans created the Cylons, robotic beings, to make life easier. They rebelled and a war was held. An attack was done to the 12 colonies, and the humans joined a fleet of ships lead by Commander William Adama of Battlestar Galactica to the legendary 13nth colony: Earth.
I started watching BSG about a month ago and my impression on it is that it is awesome! The miniseries, considered a backdoor pilot, is an awesome start. The miniseries is great. So awesome and so full of action. If you want to start watching BSG, then start here.