mail sheet triggered by date

I have uploaded a sheet, that tracks drivers lic. expiration dates, I need it to send e-mail when the drivers lic is 30 days from expiration. I have been here

http://www.rondebruin.nl/mail/folder2/mail2.htm

I read through how to copy and paste this code in my workbook but I don't understand where / how I point this at a cell so when the cell = 30 it sends the mail. I can see all the other where the email address goes, TO, CC, Subject, Body, but van't figure out the trigger part or where it is or if I have to get more code for that.

Thank you
Ken