Use this site.
www.good-tutorials.com
It's really good. I basically learnt how to use photoshop off there. Start with trying a few of the tutorials creating an effect or whatever, and you'll gradually get to know how photoshop works and you will be able to use the tools to make something up yourself. =) of course, experimenting yourself is always the way to go, but I sometimes find it good to follow some tutorials to get an idea what you can do in photoshop.
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