Psychologists have a PhD and are trained in academia and research besides the clinical practice of psychology. They can have any of a number of specialties such as clinical psychology, counseling psychology, school psychology, social psychology (which is a research field - social psychologists don't generally do therapy), and any number of specialties within those groups. Psychologists have specific training in testing and clinical assessment. There are some who only do testing and assessment. Others are therapists. Some teach.

Bachelor's level social workers can do case management and other types of social service work, but in most states are not licensed to do therapy. Master's level social workers have more training in social service (the field is sociology not psychology), and do not usually have academic training in therapy but can take electives or do internship in therapy and learn that way. They can be licensed to do therapy.

Mental Health Counselors have specific training to be therapists. This is a master's level profession (and is my degree and license). We have some training in assessment also and can develop a specialty in this area. The degree is based on psychology clinical practice.

There are also marriage and family counselors, who are trained similarly to mental health counselors, with more emphasis on couples and family counseling. They are also licensed at the master's level. They might typically have an undergraduate degree in child and family development. Although there is variation in all of the groups as to undergraduate studies, and any might have an undergraduate degree in any of these fields (psychology, social work, or child and family development), or in anything else really as long as prerequisites were met.

Psychiatrists are medical doctors and usually have focused their studies on biology. They have training in general medicine first and then specialize in psychiatric medicine. They don't have much if any training in therapy and usually no training in psychological testing. They are trained primarily to prescribe medication. If they do therapy, they may have learned those skills in a practicum or internship setting. They are medical doctors, so they are allowed to do pretty much anything they want.

There are also APRNs (advanced practice registered nurses) who have specialties in using psychiatric medicine and sometimes have training in counseling. There are some who have degrees in counseling as well as nursing. They usually prescribe medicine mostly, but may also do therapy. PAs (physician's assistants) are a similar category and work under the direction of a medical doctor. I think that APRN and PA are usually master's level but sometimes are PhD. Some states also allow psychologists to get extra training and be licensed to prescribe medication too.

Those are the main differences in training between different licenses and professions. Beyond that, individual experience and specialties vary quite a lot.