Basic Photoshop Techniques

Basic Photo Correction Tutorials:
http://www.khulsey.com/photoshop_tutorials/digital_photo-retouching_tutorials.html

Adjusting Tone with Levels:
http://www.bairarteditions.com/pages/tutorials/photoshop/exlevels.html

Learn about the Tools:
http://www.photoshoplab.com/photoshop-tool-basics.html

A bunch of Basic PS tutorials:
http://www.good-tutorials.com/tutorials/photoshop/basics