Lords of Kobol, hear my prayer...

If you're too lost (which is understandable, it's a very complex show to comprehend especially if you're coming right into the middle of it), then I would highly recommend watching the Battlestar Galactica: The Story So Far special. It gives a very informative, yet brief, overview of who the characters are and what's happening from the miniseries up until the second season finale. It's great for anyone just starting to watch BSG and doesn't know anything about what's going on.

I call Lucy Lawless's character Three because that's who she is, she's the Number Three model of the humanoid Cylons. She did inherit a human name, D'anna Biers, when a copy of her was on Galactica, but to the Cylons she's a Three. There are many copies of each model, some that have names and some that don't.