Transistion on Entry Values Question

Can a kind soul give an example of how to transistion on Entry Values? For the life of me I can't figure it out.

All I know that the documentation states "If you want to transistion an entry at a specific time, you can transition the entry based on a custom date element." That's exactly what I want to do, but how is the question! A little more help in the documentation is really needed.

I want to send an email on the due date to remind the parties involved that it's due. An on-entry Notification on the Due-Date-State is what I want. Just can't get figure out the transistion part.

Thanks for your input.

Rich