Choose a base name
Transports are tiny scripts sending a measured quantity from standard input. They are specific to MRTG Online protocols.
Add cron jobs
Paste the following to your crontab:
read VALUE ; wget -q --post-data="value=$VALUE" \
-O /dev/null -S "http://mrtg.prcn.co.cc/u/$1"
Wait for 5 minutes
Empty graphs will be created
Wait for 5 more minutes
First data will show
Enjoy
Note that this setup is "quick and dirty": anyone can in principle see your graphs and even add data points on your behalf. You should upgrade to a more secure setup later.