There's a ton of stuff on the net and then there's always the old fashioned way - read a good book. Scott Kelby and Brian Peterson have some great stuff on understanding aperature and light and composition. As for online stuff, I like:
http://digital-photography-school.com/ by darren rowse is good for basic stuff
http://www.tmelive.com/index.php/pages/index.html by Craig Tanner, a great teacher
http://www.lynda.com/ is a great resource for Photoshop or Elements training. They offer hundreds of online video/webcast training under a subscription plan but there are a lot of free ones to try her out and see if you like her style.
Good luck!