Far different than what the movies and such portray it to be. You might want to read First Person Plural by Cameron West, PhD or A Fractured Mind by Robert Oxnam. These are both pretty typical cases of DID. But I warn you, as interesting as they are, they are nothing like the fictionalized cases you see in the movies. Robert Oxnam is internationally recognized and has accompanied people like Bill Gates, Warren Buffet, and George HW Bush and Barbara on trips to Asia as an advisor. He is a specialist on Asia and was president of the Asia society for more than a decade. Needless to say, no one ever suspected that he had DID, and he was a very functional individual. This is usually the case with people who have DID.
Another very interesting case of DID is The Minds of Billy Milligan. His case is very atypical in many aspects, very typical in others. Because of the severity of his problems, he was not functional in the way that most people with DID are.