In a template, settings can be read using the [wt:wt.settings] tag.
Example: Getting the Site URL
[wt:wt.settings.Site Details.Site URL]
In PHP settings can be read with the WTConfig::get() function.
Example: Settings the Site URL
WTConfig::get("Site Details/Site URL");
To Set a setting, use the WTConfig::set() function
Example: set the site URL
WTConfig::set("Site Details/Site URL", "http://www.siteurl.com/")