Change the variables at the top to match your setup. Most should be just fine as they are, but you can change them should you need to.
Line 27: add the local and remote IP addresses before $PPP_OPTIONS
Line 31: Change this line, and the two after it to set routes for your internal nets.
While bash scripts are generally stable, they have been known to fail. In order to make sure that the vpnd script keeps running, add an entry to the client's crontab that runs the check-vpnd script. I run mine every 5 minutes or so. If vpnd is indeed running, check-vpnd doesn't use much CPU.