Some basics:

What is a psychiatrist?

A psychiatrist is a physician who went to medical school, then did an internship, then did a residency specializing in psychiatry, and, finally, may have done extra-training. His after medical school training was almost always performed in connection with a hospital or mental institution. He is carefully supervised during this period.

A psychologist is a university trained person who gets a Ph.D. in psychology. He has to write an original thesis. This is reviewed by a committee for its originality and contribution to the field. He may get his degree in clinical psychology or research psychology. He may or may not have extensive training in brain and body functions. After graduate school, he or she may get special training in therapy or dealing with mentally ill patients. There is a one year internship at some hospitals for psychologists, but this is not required for a license in some states.

A Social Worker gets a degree from college in social work. She or he may get a masters degree and then special training in therapy.

A therapist is someone who sees patients and gives counseling in the form of psychotherapy, cognitive therapy, or simple instruction. A therapist can be a psychiatrist, a psychologist, or a social worker. There are other types of professionals who do therapy but, usually, they are lesser trained. An exception may be a nurse practitioner who has had special training in therapy at an accredited institution. Only the psychiatrist can give medication (The exception to this is in New Mexico where psychologists are given that privilege. In some cases a nurse practitioner may also give medication.). All types of professionals mentioned above can do therapy of various sorts. The skills of each are quite varied.

These categories tend to be very confusing for the average person, but they are what they are.