This is explained in the following Technet article, it is loosely coupled enough to wrap any suggestive business scenario around it that requires approval prior to a page of content being published on a publishing site...http://office.microsoft.com/en-us/sharepoint-designer-help/understand-approval-workflows-in-sharepoint-2010-HA101857172.aspx
Regards John Timney http://www.johntimney.com