Supaplex, mostly forums at first. It took me a long time to understand ANYTHING looking back. I would post hands and my stats and stuff for people to criticize. I would recommend doing that at liquidpoker.net in the small stakes forum. That's how I started learning. 2+2 is an option too, but the bigger community made it hard for me to sort the bad info from the good info at first.
One thing I definitely recommend in regards to 2+2 for someone starting out online poker, is going to the low stakes NLHE forum and reading some of the stickied threads. There's some invaluable information in them if you take it to heart.