Hello nice to see you posting again...The DSM is a book like a dictionary. It tells the names of all the mental disorders in the USA that treatment providers treat what each mental disorder is, and what treatment providers look for..

example I had DID. when the psychiatrist was testing me to see if I had that mental disorder he knew from reading the current book of the DSM what symptoms to look for to see if I had DID.

kind of like a medical doctor has a dictionary called the Physicians Desk Reference to look at when they are diagnosing medical problems.

and like a student has a webster's dictionary to look at to help them spell and know what words are.

the number in the books name is how many times the book has been rewrote, revised, changed.. the DSM is being completely rewrote for the 5th time.