According to Freud's theory, what is the essence of dreams?

Freud wrote The Interpretation of Dreams: Dreams, as a part of people's psychological activities, are not mysterious or illusory phenomena. They are special manifestations of complex psychological activities in the human body, and their roots, like the rest of human psychological activities, are deeply hidden in the subconscious mind of the psychological world; This kind of subconscious is neither the "manifestation" of the soul nor the "revelation" of the "God" outside the human body, but the concentration and precipitation of early human practice. No matter from the individual or the human race development series, in the final analysis, it is the product of practice.