What with the various Crises in the DC Comics universe(s) in the past 20 years or so, it’s pretty hard to figure out what’s what with all the retconning. (See Crisis on Infinite Earths, Identity Crisis, Infinite Crisis, plus Zero Hour and other bizarreness.)
Post Infinite Crisis DC Comics produced a serialized (new) history of the universe to bring everyone back to speed. It’s not gripping, nor exhaustive, but might just make everything a little clearer (especially when you’re trying to figure out just which Superboy, Hawkman or Flash is being talked about.
See DAILY PLANET 52 WEEK SPECIAL: History of the DC Universe (Part 1). Should be 10 parts when all done, I think.