DME is two things when you arrive at MCO -- a free bus ride to your resort, and AUTOMATIC luggage delivery to the inside of your resort room, whether you're in the room or not.
You need to make reservations for DME. About 3 weeks before your trip, you'll get a DME information packet. Included in this packet are DME luggage tags. These luggage tags are NOT plastic things that you have to write info onto. DME luggage tags are sticky paper. You know the luggage tag the airline puts on your luggage at the airport, the tag with the 3-letter airport code on it? DME tags are made of the same paper, but are thinner and are bright yellow. They are pre-printed with all kinds of info.
After your luggage leaves the airplane, special employees look for the luggage with the DME tags, and grab those bags out of the stream of the regular luggage, before it gets to the baggage claim carousel. So if you have DME tags on your bags those bags will never make it to baggage claim. As I said, they get pulled "behind the scenes," and from there the luggage is loaded in trucks and transported to the various WDW resorts.
When you get off the plane, you go straight to the DME Welcome Center. It's in the same area that rental car companies' counters are located. You wait in line at the DME Welcome Center, then check in, and then you're told which bus queue to get into. The queues are inside. When your bus is ready to board, you'll be led out to it. DME is a shared service. There will be no more than 4 resorts on the bus, which means no more than 3 others and yours. There's no set groupings of which resorts go together, it's all done based on the need at that exact time.
You can take your carry-ons into the bus with you if they'll fit under your own seat, or on the overhead shelf. If not, you'll need to have the driver stow them underneath the bus. The buses are plush, touring motor coaches. There are viedo screens and you'll watch a "Welcome" DVD.
At each resort, the driver will unload people's carry-ons, and you're on your way.
People DO have the option of NOT putting the DME tags on their checked luggage, going to baggage claim, waiting for it, schlepping it to the DME area, then to the bus, etc., where the driver will stow it all underneath the bus. To me, this option is a waste of time and energy, and gives up one of the great perks of DME.
Your DME-tagged luggage will arrive 2-3 hours later. So pack accordingly in a carry-on for what you'll need at first. Actually, this is a good strategy to follow no matter where you fly, in case the AIRLINE delays your luggage.
You DON'T need to be in your room when the luggage arrives. It will "magically" appear whether you're in there or not. The Bell Services CMs who deliver this luggage are already "pre-tipped" by Disney, so even if you are in the room (which you shouldn't be, you should be out playing!!!

), you really don't need to tip that person, as funny as that may make you feel.
A day before you leave WDW, you'll get info about your DME bus pick up time for the next day. SOmeone else will explain departure procedures, or I'll do it later, I gotta go help my son.
HAVE FUN!