Even though many of Freud's psychological theories have been discredited, Freud played an integral and massively important role in the development, progression and fame of psychology. Freud is the father of psychoanalysis, which is a branch of psychology that focuses mostly on the concept that many of our deep psychological issues lie buried beneath accessibility, in our subconscious. Any trauma, mental illness, hang-ups or issues that one has are contained within the subconscious mind, and can be accessed only through intensive psychotherapy with a trained psychologist. Freud believed that in order to understand yourself, you had to dig deep and bring those issues to the surface in order to analyze them. He used dream interpretation (writing one of the first books on dream therapy, called "The Interpretation of Dreams" which is still widely read today), hypnosis, transference, stream-of-consciousness sessions, and free association in order to access people's subconscious.
In addition to founding psychoanalysis, which is still in practice on a very large scale today, Freud also came up with numerous psychological theories that at the most effectively explained human behavior, and at the least sparked widespread controversy that helped people to discuss solutions and issues. He developed the "Oedipus complex," which suggested that all children are secretly in love with their opposite sex parent, and hence want to kill of the other parent. Tagging along with this highly controversial theory were other child development theories that all centered around oral and genital fixations, stages that all children go through in their development. From these theories stem the now widely-used terms such as "oral fixation" and "anal-retentive." He also came up with the famous ego, id, and super-ego concept of human behavior, the id representing animalistic desires, the super-ego representing societal constraints, and the ego being the mediator between the two.
These comments refer to just a small portion of Freud's contributions. I can confidently assert that Freud is the most discussed psychologist of all time, whose contributions to the field surpass any other's in terms of influence, controversy and impact. I hope that those thoughts helped a bit; good luck!