DDP and DDE are two completely different things. DDP is the dining plan that uses CS and TS credits.
DDE is the Disney Dining Experience and it only applies to AP or Florida residents. It is a special card that eligible people can purchase and is good for one year and 20% off of food and drinks at select restaurants in WDW. If you are only interested in adding the dining plan on to an upcoming trip, the DDE is of no significance to you and you should just ignore it when you see it.
Hope that clears it up a little for you.

Good luck with your planning!