In the preview pane in Font Book, you can see all of a font's characters. But, let's say I want to use a particular one of them in another program. How do I type the character that I want?
You can use the Character Viewer in 10.6 (System Preferences>Language & Text) or Character Palette in 10.5 (System Preferences>International). And in InDesign you can also use Type>Glyphs to open the Glyphs palette. There are other ways too.