Adobe Photoshop is one of the most powerful image editing tools available. Many people stick with the tools they get with a digital camera, but if you have the money to spend, Photoshop is an incredibly versatile and potent tool.
The folks at Photoshop Roadmap have put together a list of free tutorials (training) for specific tasks you might want to perform - from the easy (removing red eye) to more difficult (removing wrinkles, changing a person's facial expression).
Here's the link...scroll down past the ads up top and you'll find tons of tutorials that might be of use!
Link to site