What exactly do therapists do?

What kinds of problems would someone go to a therapist for? What kinds of questions do they ask and what are peoples’ goals for going to someone like a therapist?

What is the difference between a therapist, counselor, psychologist, etc? Which of the above can write prescriptions for anti-depressants or anti-anxiety meds?

Any other information? I’m considering going to one but actually unsure of their function.