Power level is very confusing. You can make a very high-powered bardbarian by giving her a ton of Skill Power, but skill power is useless for her, so she'll actually be quite weak.
Runes are an advanced feature of the game. To some players (like me), they're the best part of the game. To others, they're just overwhelming. Fortunately, there are some useful online guides. I've written one, which has links to the others.
My guide explains rune colors, primaries and tertiaries, as well as how to pick good runes.
As for CDR, that means Cooldown Reduction. It speeds up many green, blue and purple skills, which can make some heroes far more powerful (without, incidentally, increasing the "power" number very much). Cooldown Reduction has a cap of +50%, and reaching that number is very much worth it for some heroes -- Ninja and Thief come to mind right away.