Preferences are used as TWikiVariables by enclosing the name in percent signs. Example:
When you write variable %WEBBGCOLOR% , it gets expanded to #FFD8AA
The sequential order of the preference settings is significant. Define preferences that use other preferences first, i.e. set WEBCOPYRIGHT before WIKIWEBMASTER since %WEBCOPYRIGHT% uses the %WIKIWEBMASTER% variable.
You can introduce your own preferences variables and use them in your topics and templates.