To have rtgpoll start at boot time, you must edit 
${SYSCONFDIR}/rtg/rtg.conf
and insert the following in /etc/rc.local.

  if [ -x /usr/local/bin/rtgpoll ]; then
	  echo -n ' rtgpoll'
	  /usr/local/bin/rtgpoll -t target_file \
	      -c /etc/rtg/rtg.conf >/dev/null 2>&1 &
  fi

This will start snmpd and use ${SYSCONFDIR}/rtg/rtg.conf for the
configuration. Be sure to read the manualpages of rtgpoll(1) and
rtgplot(1) to create a target_file. 

Example files for the webfrontend of rtgplot have been installed to
/usr/local/share/examples/rtg/web/.

Example files and a Database creation Script have been installed to
/usr/local/share/examples/rtg/etc/.