How to use the OS X character viewer – CNET

The keyboard offers a number of common characters for the language layout you have chosen, especially when you use modifier keys such as Shift, Command, and Option to invoke alternative character sets; however, while those that are mapped to various keys are common, they are only a minor subset of the characters that are available for you to use when composing documents.

via How to use the OS X character viewer – CNET.