On the proxy server two program (pproxy and ringd) will be running.
You should have a file named pproxy.rc in the /etc/popular directory. Sample files can be found in the conf directory of the POPular distribution. Make sure pproxy.rc is executable.
First start ringd as user 'root'. ringd will run in the background and bind TCP ports for pproxy because pproxy runs as a normal user.
Next start pproxy as the user and group you chose. You should see some log messages appearing in /var/log/popular/pproxy.
To configure the running pproxy use the pcontrol program. Always start pcontrol as the user you have chosen for the pproxy. If everything is set up properly you can just call /etc/popular/pproxy.rc to do the first configuration.