Introduction to Adobe Photoshop
http://www.extropia.com/tutorials/photoshop/toc.html

Extropia

Abstract:

Adobe Photoshop is hands down, the most popular program for creating and modifying images for the Web. This is true not only because Photoshop is available on a wide array of platforms ranging from Mac to Windows to UNIX, but because after four generations of development, Adobe Photoshop has the most intuitive user interface, the most complete set of tools, and the largest number of reference books around.