Andre Breton defined the surrealist movement as,
Pure psychic automatism, by which one intends to express verbally, in writing, or by any other method, the real functioning of the mind. (Gardener’s Art Through the Ages page 1074)
He means that the surrealists were trying to express the pure truth that exists in the mind only when in a dream-like state. They believed that it is only in a sub conscious state when the conventions of customs, culture, and environment no longer get in the way, and we can see into our deeper self.
The surrealist artists used perspective tricks and strange imagery to pull the viewer into a subconscious experience. An example of both these methods can be seen in Salvador Dali’s The Persistence of Memory.
They also used a technique called automatic writing and drawing which is defined by the eNotes/Wikipedia page on the subject as “a process in which a person writes something, usually by hand, supposedly without conscious thought of what they are writing” an example of this technique would be André Masson’s Automatic Drawing. When artists used this technique they were trying to tap into their subconscious and reveal truth.