Applications such as Apple Mail, BBEdit, Eudora, TextEdit, and many modern applications support OS X Services.
Note: Some applications do not support Services. If the Services menu is completely grayed out when you have a text selection, then the application likely does not support Services. An example of this is Microsoft Word.
The Services menu can be found in the application menu, such as "TextEdit". Once installed (via Preferences), you can use TextSoap in other applications through Services:
Services only works when text is selected and the text is editable. In Apple Mail, Services only works on outgoing messages.