Short answers, pulled from the story.
Clinical psychology is generally considered to have begun in 1896 when Lightner Witmer opened the first psychological clinic at the University of Pennsylvania. Witmer coined the term "clinical psychology" in 1907 in the first journal of the field, The Psychological Clinic.
Clinical psychologists are experts in psychological assessment, including neuropsychological and psychometric testing, and treat mental disorders primarily through psychotherapy. Psychiatrists are licensed medical doctors who can prescribe psychotropic medications, order laboratory tests, and use medical procedures such as electroconvulsive therapy (ECT) or transcranial magnetic stimulation (TMS), but do not typically have advanced training in psychometrics equivalent to that of clinical psychologists.
The Doctor of Psychology (PsyD) is a practice-oriented doctoral degree formally recognized at the 1973 Vail Conference on Professional Training in Psychology. It emphasizes clinical theory and practice over research, similar in structure to professional degrees in medicine and law. The first program explicitly based on the PsyD model was established at Rutgers University.
World War II dramatically expanded the scope of clinical psychology by creating an urgent need to treat veterans experiencing psychological trauma. The Veterans Administration funded large-scale doctoral training programs, and by 1950, more than half of all psychology PhDs in the US were being awarded in clinical psychology, up from no formal university programs in the field in 1946.
The four main schools are psychodynamic (derived from Freudian psychoanalysis, focusing on the unconscious and transference), humanistic or experiential (developed in the 1950s through Carl Rogers and others, emphasizing unconditional positive regard and self-actualization), cognitive behavioral therapy or CBT (targeting the interaction of thought, feeling, and behavior), and systems or family therapy (treating the family or couple as the unit of treatment).
In most places, clinical psychologists cannot prescribe medication. In the United States, eight states, Louisiana, New Mexico, Illinois, Iowa, Idaho, Colorado, Utah, and Vermont, allow clinical psychologists with advanced specialty training to prescribe psychotropic medications. Psychiatrists are legally authorized to prescribe in all US states and Canadian provinces.