To have radiusd start at boot time, you have to adapt
${SYSCONFDIR}/raddb/radiusd.conf and insert the following into /etc/rc.local.

if [ -x ${PREFIX}/sbin/radiusd ]; then
	install -d -o _freeradius /var/run/radiusd
	echo -n ' radiusd';	${PREFIX}/sbin/radiusd
fi

This will start radiusd and use ${SYSCONFDIR}/raddb/radiusd.conf for the
configuration. Example configuration files can be found in
${PREFIX}/share/examples/freeradius.