I've participated in a couple of threads on DPreview and Photography-on-the.net this week that were basic discussions about sharpening digital photographs. After posting a video segment that discussed why we sharpen, how sharpening works, and how to approach sharpening in a systematic way, I'm still in a mood this weekend to help educate digital photographers on sharpening basics.
This is Chapter 2 from my eBook/video on sharpening, Sharpening Your Photographs. The title of the chapter is "Sharpening Tools." The .PDF is nearly 90 pages long. It covers each of the sharpening tools available in Photoshop CS and later. You don't need Photoshop to benefit from this chapter. The discussion in this chapter is applicable to any photo editor that includes sharpening tools like Unsharp Mask.
The chapter explores the tool settings, but it goes much further. For example, there are detailed explanations and illustrations of how Amount, Radius, and Threshold work for sharpening tools. Most users have a fuzzy idea about how the sharpening tools work. After you read this chapter, you'll have a much more solid foundation for sharpening your photographs.