Although it is older and the terminology has changed from MPD to DID this book(let) at 46 pages can be one of the simpler ways of presenting infomation to those who cannot grasp the complexities explained in other books and literature.
United We Stand ISBN: 0-9613205-9-1

order form for Echolalia Press

There are many other books with different approaches but based on your posts and your request of not too confusing we'd say start with this one and go from there.

kindly,