A Central Server is a Rocks Frontend node that can kickstart other frontends and provide rolls over the network, in a process called WAN kickstart. All Rocks frontends have the ability to act as central servers.
The standard Rocks distribution (located under /export/rocks/install) contains a distribution suitable for WAN kickstart. The only steps you must take is to open "www" and "https" access on your frontend for the purpose of RPM package transfer. See Enable WWW access.
You may wish to serve rolls from your central server that you have not installed on your central server when the central server was initially installed. All frontends will serve the rolls they were built with to client frontends, but often it is advantageous to serve other rolls as well.
First, you must download the Roll ISO image to your central. Then, execute:
# rocks add roll <rollname>*.iso