I wonder if you can go back to Riverwood and find the guys to show you the stones. I'll try that today.
A buddy of mine said destruction spells get almost too powerful once you get them to 80-90%. They cause too much collateral damage, so you can't have a companion or use the spell when townsfolk are around or you will kill them all.
I think the shouts serve as a kind of magic for non-mages, but the destruction spells are too powerful not to master. Right now I use sneak and archery to attack, then switch to sword/shield/magic when they get in close. I don't like that you can't really hide once enemies start looking for you. Or maybe my sneak isn't trained up enough.
Here's my character, I'm lvl19 now (I removed his elven helmet of eminent archery for this photo):
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