Well... My advice would be to come up with some projects to do, then try to do them with Photoshop. When you get stuck, refer to the manual/help files. If that doesn't do it, try doing a google and/or forum search for what you're trying to accomplish. If you still are stuck, then come on in and post a question about your specific problem. We're always glad to help.
There aren't a whole lot of "how does photoshop work" type tutorials online, since most people pretty much expect you to have read through the manual and know at least a little about the program. If you need something super basic, I would suggest picking up a copy of Photoshop Classroom in a Book. It's a great, project based, beginner's guide that walks through most of the features of photoshop.
Hope that helps somewhat. As I said, if you're stuck on something specific, post a question!
Welcome to the wonderful world of Photoshop.