You should have a file named pserv.rc in the /etc/popular directory and it should be executable for the user you have chosen to run the server as. A sample file can be found in the conf directory of the POPular distribution.
Decide where to put the mailboxes, the sample config file uses the directory /pop for this. All mailbox directories must be readable and writeable by the user you chose for running pserv.
Start the server as the user and group you chose: pserv. You should see some log messages appearing in /var/log/popular/pserv.
To configure the running pserv use the pcontrol program. Always start pcontrol as the user you have chosen for the pserv. If everything is set up properly you can just call /etc/popular/pserv.rc to do the first configuration.
If you want to use the pcheckd daemon, start it as the same user you used for pserv. You need at least to use the option -m to tell pcheckd where the mailbox directory is (/pop by default).