Freud's wish-fulfilment thesis begins with the clearest cases: convenience dreams, thirst dreams, and the unambiguously satisfied wishes of children. A child denied a boat trip dreams of sailing; a man who ate anchovies before sleep dreams of drinking cool water. These dreams carry their meaning on their face — they are simple, direct wish-fulfilments that disguise nothing.
Adult dreams are more complicated because the wishes they fulfil are unacceptable to the waking ego: they are aggressive, erotic, or infantile in character. The dream cannot present them directly without arousing the anxiety that would wake the dreamer. Instead, the dream-work transforms the latent wish into the bizarre, innocuous, or frightening manifest content the dreamer consciously recalls. What appears as a nightmare may be a censored fulfilment — the anxiety being the signal that the disguise has partially failed.
The claim that anxiety dreams and punishment dreams are also wish-fulfilments is one of Freud's most provocative moves. Even here, he argues, a wish is being satisfied — not the wish of the dreamer's ego, but a wish from the censoring agency itself (what would later become the superego), which wishes to punish. The dreamwork's ingenuity is inexhaustible: every dream satisfies something.
The wish-fulfilment thesis is the core of Chapter III of The Interpretation of Dreams, extended to cover anxiety dreams and punishment dreams in Chapter IV.