All the details are here.  But in a nutshell:

• It must be turned on for each file via the command line.  For my project I issued:

svn propset svn:keywords "Revision" PuffinApp.rc

• The setting is stored in the database so it doesn’t need to be done on other clients
• You must enable for each keyword desired.
• Keywords include: Date, Revision, Author, HeadURL, and Id (a brief synopsis)

Update 11/10: Cornerstone has the ability to add these directly.  Go to the Properties tab on a file and look for the Keywords field.  The key icon just below the field is there for easy entry.