Councilor can be just about any one with compassion and knowledge. Therapist have to have a couple years of college Psychiatrist is an actual medical doctor who specialises in mental health and they have the ability to prescribe medication if they believe you need it.
A Counselor is a little like a Psychologist, but can basically be anyone. Just like what yinandyang said. They bring comfort to you and will be there for you.
A Therapist helps you get back on your feet after an accident or if you suffered from an eating disorder.
A Psychologist specializes in mental health and they can sometimes have the ability to get you thrown into a mental hospital if they find that you absolutely need it. Other than that, you can volunteer to be in one if you find yourself mentally ill.