Psychology refers to the general study of all that pertains to the mind and brain. Most psychologists have attended graduate school (not medical school) and usually have attained a Ph.D. or Psy.D. They also use the prefix of "doctor." The Ph.D or Psy.D means they have studied and trained beyond the level of a master's degree, usually including practical experience treating patients in psychotherapies of some kind. They have also received significant specialized training in psychological testing. They may have studied psychiatric medications, however they are not legally allowed to prescribe medications; otherwise they may be just as qualified to evaluate and treat (with various forms of psychotherapy) many aspects of the problems of mind, brain, or personality.
Psychologists often subspecialize in certain age groups and/or certain types of psychotherapy. Sometimes they specialize in certain types of psychological testing.